If you decide to swap brakes I'd swap the entire rear axle for a 14 bolt from a dual wheel "cab and chassis" GM pickup. That model is the correct width, then run single wheels on it.
Additional advantage is you can pick from any number of gear ratios, and they're cheap.

•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
---All pictures---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-