Any updates on the progress? I have the same problem with the brake kit I put on my 1070 Mercedes. Mustang II front end to fit the Ford 4.6L V8, CPP brake kit and 7" dual diaphragm booster with 1 1/8" Corvette master cylinder.
Brake peadal is hard as a rock but can't stop for crap. Changed to EBC pads which helped but not enough. Considering going to 1" master cylinder and adjustable proportioning valve but was hoping to get a report back before I spent the money. By the way in a hard stop I have about 1000 PSI for the front calipers. Have not been able to measure pressure at the rear because I don't have an adapter for the Mercedes calipers on the rear axle.
So, any update?