[Tom Goldman]

As was mentioned pedal ratio is critical .If the car originally had power brakes the ratio was only around 4 to 1 ,a ratio of 6 to 1 is considered ideal . also ,If you are only using discs on the front and retained the drums on the rear ,a master cylinder with a smaller bore will help.
On a disc /drum car I usually use a 1 3/32 bore master cylinder which wit the 6 to 1 pedal usually will yield around 1000 psi with reasonable pedal pressure.