Mustangs dont have hydraulic clutches? are you positive? I know my old 89 had a standard "hard as hell" clutch, but my 99 clutch always felt so soft and I just assumed it was hydraulic. If not then how do you adjust it?
MY 99 has a mechanical clutch, for sure u can adjust the pedal if u need to, put your foot under the pedal and lift up till you hear a click, then push it all the way down to the floor and that is supposed to adjust the engagement point and stuff like that.
On my old celica you could bleed the hydraulic clutch on the salve cylinder in the engine compartment. Your 89 probably had an after market pressure plate, that is wht it was so diffficult to push. I drove a 90 5.0 that had a real stiff clutch but the kid put an aftermarket clutch into it.