C5 brakes/ master cylinder issues

[vette427-sbc]

I just finished fabbing up some C5 front brakes and LS1 rear brakes on my fathers '55 Chevy. We used a C5 master cylinder and a wilwood adjustable proportioning valve. Also using an 8" dual diaphragm booster.
Heres the issue:
The car stops, but not great. The pedal goes down pretty far, then gets very hard. Doesnt feel like there is air in the lines either. It just doesnt stop like I would think it should. The pads are Hawk HPS front and Napa premium rear pads. Rotors are new as well. We made a few gradually increasing hard stops to bed the brakes and it helped a little bit, but they still arent "biting". Are most brake pedal ratios the same or at least similar? I would have thought the C5 master would be perfect with the C5 fronts and LS1 rears. Do I need more break in time for the pads to bed into the rotors?

Heres a few pics: