The rear engine mount crossmember is made up of a few pieces.
When test fitting consider you may be able to use the smaller pieces from your original with the main member form the 54. I can't say for sure this is useful, but worth checking.

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-