Without being a brake systems engineer it's difficult to say what is safe to change...
If you match wheel cylinder sizes with a similar model truck and use same master cylinder that truck used you'd probably have the ratios of fluid volume or stroke about right.
Generally not a good idea to swap brake components around without a full understanding of what's going on, brakes are very important.

•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-