this is a 1971 Chevelle with a 350 motor and auto trans.
Did the converion using the correct prop valve..but it was used.
replaced the rod that goes from the mc to booster with the short one
car stops ok but the pedal is hard..doesn't feel like there is much power
assist for the disk brakes..any help???

check your vac source,,off the manifold usually works pretty good,sounds like you may not have enough vac....

go to MPbrakes.com. Their web site had great info on brake problems.