I think you'll find the rusty one has 2.5" brakes.
Thanks for the spring link. I should find the detailed specs for the 1.5 ton springs because I have a pretty good 2 ton set which after removing a few leaves might can reconfigure to be same as 1.5 ton.

•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-