Working on a 71 E-body for a guy; has a rear disc brake swap on an 8 3/4. It has the GM Eldorado calipers it appears, the ones with the parking brake cable built into them. On the front, has 11" single piston discs.

Brakes are working, but poorly. First half of pedal nothing really, last have it brakes but just not as good as it should.

I looked it over, does NOT have a prop valve on it; and it appears to have a stock rear drum front disc master on it.

Anybody know what MC should work with this combo? Will the stock one work with a prop valve? Should I add adjustable prop valve from like Summit on the rear line to fine tune the setup? (I run one on my 1st gen Cummins w/ a disc swap; and on my Dart with good results).

Thanks as always.