"What would you guys do in my shoes?"

Not knowing much about how your truck is configured and your fabrication/engineering skills, I would advise going to people who specialize in brakes.
In my area (I have no idea how good they are):

MASTER POWER BRAKES
110 Crosslake Park Dr.
Mooresville, NC 28117
1-800-472-4181
[email protected]

People have converted to dual non-power master cylinders on drum-drum trucks using newer generation master cylinders. Disc-drum started around 1971 and for this master cylinder you would need a proportion valve. If you have a drum-drum system, compare the size of your wheel cylinders and find/determine which master cylinder works best for those sizes.

I don't like giving advice on steering and brakes systems because they are extremely important for safety reasons.

"Adding CFM to a truck will only help at engine speeds you don't want to use."
"I found there was nothing to gain beyond 400 CFM."