What disc brakes did you use? When I did the Granada brakes on my '65 Mustang, I used the granada proportioning valve and used a 1976 or 1977 Granada MANUAL disc brake master cylinder and it bolted up to Mustang just fine with no mods, it should bolt up to your car without problems either. The brakes on the Mustang feel about as good as power brakes!
I hope this may help you out.
By the way, The disc brake setup off the granada was actually off of a power brake car, but I had a problem fitting the booster that was on the Granada.