1 ton, a GMC model 250, will have 137" wheelbase and if a pickup truck it has a 9' bed (4 stake pockets per side). The frame rails behind the cab are also flat on top.
A 3/4 ton has shorter bed and often slight hump in frame over rear axle.
Both have 8 lug wheels, and springs may have been changed or perhaps special ordered differently than expected.

•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-