My install is the GT2008-FT-MII kit on a 1974 Pinto using Bullitt wheels.  I have all the components to try both the 12.5" and 13.2" brakes and I have several thicknesses of spacers to try.  

The pedal is 10" from pivot to center of the pedal and the mc pushrod is 1.810 center to center of the pivot which gives it about a 5.5 ratio. I have a '94/'95 Mustang Cobra mc with a 15/16 bore that I was  considering using because the stock pinto mc has a 15/16 bore and the stock single piston calipers actually have more area than the combined area of the dual piston mustang calipers. With this logic, wouldn't going up to a 1" give a firmer pedal that requires a little more effort? The pinto caliper piston is 2.6" which gives 5.31 sq-in area and the mustang pistons are 1.68" which  give 2.22 each x2=4.44 sq-in area per caliper.  Please correct me if I'm wrong, because since my pedal is shorter than the mustang pedal (12") I don't want any firmer than I really need.  Thanks again!!!

Absolutely, I totally understand the leverage. That's why the caliper is the same for multiple years of late model mustangs, but the rotors are larger diameter on GT models for increased braking.  Heck, I'm going from a 9" rotor to either a 12.44 or 13.2 depending on which fits in the wheel.  The stock wheel diameter is equal to the new rotor diameter,   Thanks again Steve!

Thank you. I've got plans for it, but time is the most valuable commodity. I am looking forward to the front brake upgrade! It's already got a one side narrowed explorer rear end in it. I'm just debating on using the explorer solid discs or the '05 up mustang vented rear brakes (e-brakes hook up much easier). I believe the only thing I'd have to do to get the mustang brakes to work on the explorer rear is to bore the rotors .020 or turn the step back on the axle.  The explorer axle has the standard 2.780 wheel locating diameter, but it steps up to 2.800 for the rotor locating diameter. They both use the same 2.5 spacing and the same backing plate pattern.