The frame on a 4100 is very much like the 3800 with exception of bumper brackets/frame extension up front and running board brackets. If you end up with both trucks you might find swapping some 1 ton parts to the 4100 gets you where you're trying to go.

The fenders and hoods are different between the two models, and the rear axle and some of the front axle/brake components.

Grigg

•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-