I could be wrong but I thought Mustangs had self adjusting clutches and that if you hooked your foot under the pedal and lifted it would adjust itself.
How do you know if a clutch is slipping? If you go WOT in a higher gear, 2nd or 3rd, and the rpm go up, but the tires are not spinning and you are not accelerating, then the clutch is slipping. If you pop the clutch in first and the rpm go up but the back tires do not spin then the clutch is slipping.
My experience has been that a slipping clutch is fairly obvious. Mostly clutches are engaged or not engaged. A slipping clutch is one that is fully engaged but acts like the pedal is half the way down.
ProCharger P-1SC, 9 psi, STD 396/383; Uncorrected 388/375; SAE 383/370.