Uhhh....
UNboosted master cylinders are often a poor choice for a 4 wheel disc arrangement because the calipers need more force than the driver can provide. The booster makes it possible.
I have tried 4 different master cylinder sizes when I've tried to make a manual MC work with 4 wheel discs. All of them gave an hard pedal with far too little braking force. I just couldn't press the pedal hard enough to slow the car in a rapid and safe manner.
Also, 4 wheel disc systems should NOT need a proportioning valve. The caliper piston count and sizing is what should determine the proportioning.
You want the fronts to have double the surface area of the rear. In short, a 2 to 1 ratio in brake force front to rear.
