Sounds like you are under the impression that there are lots of gear choices for these old trucks, and that they are readily available.

You will find this is not true.

You are in luck because you have a 1/2 ton, and the demand is such that aftermarket fast (3.55) gears were made, and may still be.

here is a tech tip on installing them
http://www.stovebolt.com/techtips/rear_end/index.html

And where to get them http://www.patricksantiquecars.com/

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-