Joep, in your clutch what's important is the final result: the disengagement distance at the flywheel. You check this with a flat feeler gauge thru the ventilation/inspection hole in the top of the bellhousing. A helper holds the clutch pedal to the floor while you reach in between the friction disc and flywheel surface. A few Panteras will gauge at 0.040" (equals 0.020" on each side of the disc). Most will be less. Using a too-thick clutch disc will force massive adjustment of everything for barely enough clearance. Some combinations of parts simply will not fit. This is why DeTomaso hammer-flattened stock clutch disc marcels- for more clearance. Leaving out the steel engine plate between block & bellhousing will change clearances, too. The cast steel bellcrank lever on the bellhousing can be shifted by one spline for more clearance if needed but also changes disengagement distance a little due the altered operating angle to the slave.
0 .020" clearance (per side) at max pedal travel is barely enough to separate the drive components without too much drag on the ZF synchros, which are difficult and expensive to service. Syncho assemblies include the mating gears & integral synchro cones which is why they're so ridiculously expensive! There's usually 0.020" or more run-out tolerance in clutch components. So inspect every single part of the whole clutch system for slop due to wear, age and replace doubtful parts. The linkage is all steel-on-steel and was never lubricated- likely not even from the factory. The over-center linkage upgrade in mid-'72 reduces pedal effort and can be retrofitted but adds 5 or 6 more steel-to-steel pivots that also wear & produce slop! Some owners meticulously add bronze bushings & hardened pins everywhere to remove slop.
What Can Help
Pair a slightly smaller ID slave cylinder with a stock master (the basis for so-called long-throw slaves), or a slightly larger master with a stock slave changes the hydraulic leverage and thus the clutch movement. Some long throw slaves are corrosion-proof stainless steel. Not all parts labelled 'Stock' are identical.
There are oil holes in the bell housing at the ends of the pivot cross shaft. Inside are bronze bushings that would like some oil - maybe for the first time! Early Panteras and Mangustas have needle bearings in there- also seldom lubed.
Changing clutch designs from a stock 6-spring Long clutch to a Diaphragm (GM style) clutch vastly reduces pedal force needed and may increase the disengagement distance just due to parts not deflecting with the reduced effort needed. This pays for itself in ZF repairs not needed! Diaphragm clutches are in two styles: straight-release-finger and curved finger. The flat finger type ideally needs a rounded surface throwout bearing while the curved finger one uses a flat surface throwout bearing like our stock ones. Using a flat face bearing in a flat finger clutch can produce a 'step' feeling at the pedal but otherwise works OK.
Some throwout bearings are constant-contact types and do NOT need any free play, which increases disengagement travel. This is highly desirable but when you adjust such things, be aware linkage free play (if used) changes when the engine, bellhousing and ZF all heat up. In a test, my ZF went to 185+ F degrees on a 5 hr 100 mph avg run to Las Vegas across our sparsely patrolled desert. There's more but thats enough for now.... Good luck.