I know I've seen this discussed on the forums. Have a 78 T/A. Previous owner put SSBC Force 10 calipers all the way around. It had an aftermarket dual diaphragm booster, master(that hit the hood). Proportioning valve has been replaced(not by me). Braided lines. I replaced the booster with a 1980 T/A 4wheel disc booster, and 80 model vette master. Problem is, pedal doesn't have much travel and brakes stop you...slowly. Booster is good. master was bench bled, and system has been bled 3 times. I do have a new proportioning valve that I KNOW is disc/disc that I could install.