Originally Posted by mhubert89
"The disc brake pedals are longer than the drum brake pedals and the mounting points are different. The correct brake pedal feel will not be obtained with a drum brake pedal "
You were told wrong.
The 67-73 pedals have nothing to do with whether the car has discs or drums. (On 64-66 cars, there was no difference whatsoever, all cars used the same brake pedals.)
The POWER brake pedal is longer, and mounts at the hole provided in your pedal bracket, at the top. This is true whether the car was a 200 six with power drums, or a 428 CobraJet with power discs. Same pedal. These pedals are available new.
Disc brakes came only as power boost, which has probably given rise to this misconception.
You can certainly
convert a Mustang to manual disc, and leave the stock manual drum pedal in the car. Works perfectly, and is preferred by many performance enthusiasts.