I have thought they are all interchangeable from truck to truck but the large trucks have a slower ratio (more turns lock to lock).
So with exception to the mechanism inside; the gaskets, seals, bushings, bearings, and such should be the same for all AD boxes.
I may be wrong, but this is what I remember about them...

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-