Hot Rod braking problems

[1929ModelA]

New to this site and new to hot rods. Shade tree mechanic at best. Bought a car (1929 Ford Model A Fordor) already restored (retrofitted) with no knowledge of its components finished in 1981. But what I do know is the brakes are lousy. New master cylinder mounted on frame under driver floorboard. No vacuum or other power. Sits lower than calipers. Front calipers have one piston on Mustang II front end from 1978. Rear end is from 1979 Corvette and has four pistons. I do not know the size of the bore on the master cylinder or either caliper. It has an adjustable proportional valve plumbed to the rear brakes and Wildwood blue 2 psi residual valves plumbed front and rear. Excellent pads and rotors.

The brake pedal is full and hard, not spongy but you have to press down hard to make it stop and it will coast to a stop with no skidding or throwing you thru the windshield.

Does anybody see any problems with this setup that may help me short of disassembling the master cylinder and/or calipers and provide that information? Are the residual valves the right psi given the multiple caliper piston arrangement and would they be the problem? Are they needed?

The pedal comes out of the floor, makes a 90 degree turn to the right (if you are sitting in it) then another 90 degree turn towards the driver. It does not appear to be binding in any way.