Cnc dual swing master cylinders

[gm500hprat]

I have a cnc dual swing pedal with 7/8 master cylinders on my project vehicle, gm 3/4 ton disk brakes front and rear. It's been bled brakes are soft until the bottom and then it gets hard. It won't lock the brakes up. Is this the correct size for the factory brakes. Anybody have any tips?
Thanks in advance.