I would and have used a hydrobooster and master cylinder from either of your donor trucks (disc brakes front and rear). That way you have a complete brake system from a factory vehicle, use the proportioning valve from the same and there will be no guessing about it. Only thing you might need are some 2lb residual pressure valves if not already incorporated as part of MC or proportioning valve.

Mount the assembly under the cab wherever it fits and where you can get a long push rod from the stock brake pedal to reach it.

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-