I did the exact same thing with my 69 XR7 4 speed. I found the pedal height was a little high so an adjustable brake rod was used to get the pedal lower. The pedal feel was a bit hard. I read about going to a 7/8" or 15/16" bore master cylinder would help that issue. So I did that using a 74 Maverick MC because they had factory non power front disc brakes. The feel is much softer (15/16" bore) I am considering installing a manual proportioning valve to get more braking to the front discs. I rebuilt the proportioning valve but I feel it is not doing the job correctly. The conversion was also with factory Cougar disc brake assembly from a donor car, not aftermarket. That's my 2 cents hop it helps!