A good cab dolly is a section of otherwise scrap frame from similar model truck and some scaffold wheels removable from pieces of pipe welded to each corner.
The frame already has the cab mounts in the right place.
wheels can be removed when transporting cab on dolly on a trailer.
For working on bottom of cab remove from dolly and lay cab on something soft on the back side.

•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-