In my experience older vehicles are easier to work on, they did think about these things.
Modern vehicles have so much stuff crammed in a small space they are difficult.

1939 should be easy enough.
The 1938 manual says nothing of removing the cross member to service the mounts, nor removing the cab to remove the engine.
You much be able to remove and replace the mounts without much trouble.

•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-