Master Cylinder question.

Coyote , I think I missed a key word in your original post and that was POWER. Are your disc brakes power assisted because mine are not, and that is where I believe my problem is ,trying to get the proper M/C. You did say you bench bled it and bolted it to the firewall.Did the back of the M/C you installed have two bolt holes for the piston retainer? My original also has a screw in the bottom center to hold the front piston in, which none of the replacements have had. This is # 6 now.