OK,
With that cleared up..

You don't really have an easy option to get disc brakes and keep your 1.5 ton rating and dual wheels.

You may gather a few ideas from this Tech Tip http://www.stovebolt.com/techtips/bigbolts/p30swap/

Swapping axles is one way.
Designing and fabricating your own disc brake kit is another.

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-