<Page>

                                                                    EXHIBIT 3.20

                    [Stock increased from $25,000 to $300,000
                    (30,000 sh. of $10 par)].

                         CERTIFICATE OF AMENDMENT OF THE

                          ARTICLES OF INCORPORATION OF

                       McCOLPIN-CHRISTIE CORPORATION, LTD.

     The undersigned, S. L. CHRISTIE and D. G. DINSMORE, hereby do certify that
they are, and at all times herein mentioned have been, respectively, the duly
elected, qualified, and acting president and secretary of McCOLPIN-CHRISTIE
CORPORATION, LTD., a California corporation; and, further, they do certify as
follows:

     First: At a special meeting of the board of directors of McColpin-Christie
Corporation, Ltd., duly held at the office of the corporation, 4922 south
Figueroa Street, Los Angeles, California, on October 24, 1947, at which meeting
all of the directors were present and acting, the following resolutions duly
were adopted by unanimous vote:

     WHEREAS, the board of directors of this corporation deems it to be for the
     best interests of this corporation and of its shareholders that the
     articles of incorporation of this corporation be amended to increase the
     number of shares of stock which this corporation may be authorized to
     issue:

     NOW, THEREFORE, IT HEREBY IS RESOLVED, that Article SIXTH of the articles
     of incorporation of this corporation be, and said Article SIXTH hereby is,
     amended to read as follows:

          "SIXTH: The total number of shares which this corporation may issue is
          thirty thousand (30,000); the aggregate par value of said shares is
          three hundred thousand dollars ($300,000.00); and the par value of
          each share is ten dollars ($10.00)."

     RESOLVED, FURTHER, that the board of directors of this corporation hereby
     adopts said amendment of the articles of incorporation of this corporation.

     RESOLVED, FURTHER, that the president and secretary of this corporation be,
     and they hereby are, and each of them hereby is, authorized and directed to
     present the foregoing amendment to the shareholders of this corporation for
     their approval.

                                      - 1 -
<Page>

     RESOLVED, FURTHER, that the president and secretary of this corporation be,
     and they hereby are, authorized and directed to sign, verify, and file or
     cause to be filed, a certificate of amendment of the articles of
     incorporation of this corporation all in conformity with the laws of the
     State of California.

     RESOLVED, FURTHER, that the president and secretary of this corporation be,
     and they hereby are, authorized and directed to do such acts as may be
     necessary to make the foregoing resolutions fully effective.

     Second: Shareholders of McColpin-Christie Corporation, Ltd. holding at
least a majority of the voting power of said corporation consented in writing
that the articles of incorporation of said corporation should be amended in the
manner stated in said resolutions adopted by the board of directors of said
corporation. The following is a copy of the form of written consent signed by
said shareholders of said corporation.

     "CONSENT OF SHAREHOLDERS TO THE AMENDMENT OF THE ARTICLES OF INCORPORATION
     OF McCOLPIN-CHRISTIE CORPORATION, LTD.

     "Each of the undersigned hereby certifies as follows:

     "1. I own the number of shares of stock of McColpin-Christie Corporation,
     Ltd., a California corporation, set down opposite my signature at the end
     of this certificate.

     "2. I hereby adopt and approve resolutions adopted by the board of
     directors of McColpin-Christie Corporation, Ltd. at a meeting held on
     October 24, 1947, of which resolutions the following is a copy:

          `WHEREAS, the board of directors of this corporation deems it to be
          for the best interests of this corporation and of its shareholders
          that the articles of incorporation of this corporation be amended to
          increase the number of shares of stock which this corporation may be
          authorized to issue.

          `NOW, THEREFORE, IT HEREBY IS RESOLVED, that Article SIXTH of the
          articles of incorporation of this corporation be, and said Article
          SIXTH hereby is, amended to read as follows:

               "SIXTH: The total number of shares which this corporation may
               issue is thirty thousand (30,000); the aggregate par value of
               said shares is three hundred thousand dollars ($300,000.00); and
               the par value of each share is ten dollars ($10.00)."

                                      - 2 -
<Page>

          `RESOLVED, FURTHER, that the board of directors of this corporation
          hereby adopts said amendment of the articles of incorporation of this
          corporation.

          `RESOLVED, FURTHER, that the president and secretary of this
          corporation be, and they hereby are, and each of them hereby is,
          authorized and directed to present the foregoing amendment to the
          shareholders of this corporation for their approval.

          `RESOLVED, FURTHER, that the president and secretary of this
          corporation be, and they hereby are, authorized and directed to sign,
          verify, and file or cause to be filed, a certificate of amendment of
          the articles of incorporation of this corporation all in conformity
          with the laws of the State of California.

          `RESOLVED, FURTHER, that the president and secretary of this
          corporation be, and they hereby are, authorized and directed to do
          such acts as may be necessary to make the foregoing resolutions fully
          effective.'

     "3. I hereby consent that Article SIXTH of the articles of incorporation of
     McColpin-Christie Corporation, Ltd. be amended to read as follows:

          `SIXTH: The total number of shares which this corporation may issue is
          thirty thousand (30,000); the aggregate par value of said shares is
          three hundred thousand dollars ($300,000.00); and the par value of
          each share is ten dollars ($10.00).'

<Table>
<Caption>
     "Signatures of shareholders          Number of        Date of
                                          Shares Owned     Signing
     ---------------------------          ------------     -------
                                                   
     /s/ S. L. CHRISTIE         )
     ------------------------   )
     S. L. Christie             )
                                )              800       Oct. 25, 1947
     /s/ SIGRID CHRISTIE        )
     ------------------------   )
     Sigrid Christie            )

     /s/ S. L. CHRISTIE
     ------------------------
     S. L. Christie                           1176       Oct. 25, 1947

     /s/ D. G. DINSMORE                         78       Oct. 25, 1947
     ------------------------
     D. G. Dinsmore

     /s/ E. E. HUGHES           )
     ------------------------   )
     E. E. Hughes               )
                                )              100       Oct. 27, 1947
     /s/ FLORA HUGHES           )
     ------------------------   )
     Flora Hughes               )
</Table>

                                      - 3 -
<Page>

<Table>
<Caption>
     "Signatures of shareholders          Number of        Date of
                                          Shares Owned     Signing
     ---------------------------          ------------     -------
                                                   
     /s/ G. J. FOSTER           )               60       Oct. 30, 1947
     ------------------------   )
     G. J. Foster               )
                                )
     /s/ MARGARET J. FOSTER     )
     ------------------------   )
     Margaret J. Foster         )

     /s/ H. R. JAENECKE                        185       Oct. 29, 1947
     ------------------------
     H. R. Jaenecke
                                             -----
                                              2399
</Table>
                                 - - - - - - - -

                            "CERTIFICATE OF SECRETARY

     "I, D. G. DINSMORE, hereby do certify as follows:

     "1. On each of the dates set down opposite the signatures of the persons
     who signed the foregoing certificate, I was, and I still am, the duly
     elected, qualified, and acting secretary of McColpin-Christie Corporation,
     Ltd., a California corporation.

     "2. The records of said McColpin-Christie Corporation, Ltd. show that each
     of the persons who signed the foregoing certificate owned, on the date set
     down opposite his signature, and still owns, the number of shares of
     capital stock of said corporation set down opposite his signature.

     "Dated:  October 30, 1947.

                                                " /s/ D. G. DINSMORE
                                                --------------------------------
                                                  D. G. Dinsmore"

     Third: The total number of shares of McColpin-Christie Corporation, Ltd.
adopting and approving resolutions adopted by the board of directors of said
corporation that the articles of incorporation of said corporation should be
amended, and consenting to the amendment of the articles of incorporation of
said corporation, all as stated and set forth above, is 2,399.

     Fourth: The total number of shares of McColpin-Christie Corporation, Ltd.
entitled to adopt and approve resolutions adopted by the board of directors that
the articles of incorporation of said corporation is amended, and entitled to
consent to the amendment of the articles of incorporation of said corporation,
is 2,400.

                                      - 4 -
<Page>

     IN WITNESS WHEREOF, the undersigned have executed this certificate of
amendment this 30th day of October, 1947.

                                                /s/ S. L. Christie
                                                --------------------------------
                                                S. L. Christie, President


                                                /s/ D. G. Dinsmore
                                                --------------------------------
     (SEAL)                                     D. G. Dinsmore, Secretary

STATE OF CALIFORNIA          )
                             )  ss.
COUNTY OF LOS ANGELES        )

     S. L. CHRISTIE and. D. G. DINSMORE, being first duly sworn, each for
himself deposes and says: S. L. Christie is, and at all tines mentioned in the
foregoing certificate of amendment was, the president of McColpin-Christie
Corporation, Ltd., the California corporation therein named. D. G. Dinsmore is,
and at all times mentioned in the foregoing certificate of amendment was, the
secretary of said corporation. Each of us has read said certificate of
amendment. The statements contained in said certificate of amendment are true of
our own knowledge. The signatures of S. L. Christie and D. G. Dinsmore affixed
to said certificate of amendment are the genuine signatures of the president and
the secretary, respectively, of said corporation.

                                                /s/ S. L. Christie
                                                --------------------------------
                                                S. L. Christie, President


                                                /s/ D. G. Dinsmore
                                                --------------------------------
                                                D. G. Dinsmore, Secretary

Subscribed and sworn to before me
this 30th day of October, 1947


/s/ Harold S. Nutter
- --------------------------------------------
Notary Public in and for the County
of Los Angeles, State of California
         (SEAL)