Different truck and 20 years newer.... same may or may not apply.

The 2 speed Chevy axles up to 53 (that I know of) are all geared really slow, and limit top speed, but do allow you to (slowly) haul a lot of weight.

If a 2 speed is desirable or not all depends on your use and expatiations for the truck, and what exactly is the gear ratio in high?
It's a sure thing that the 2 speed from a 51 is slow; one in a 70 may or may not be to slow, or even to fast, for your plans.

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-