Sounds like possibly some wrong parts in the linkage, or some lost motion somewhere, causing you to not have enough travel. Is it the proper Z bar, has it been modified? Is the ball stud and bracket tight, is the outer ball stud flexing in the inner fender, are the Z bar bushings in good shape? Do you have an A body bellhousing with the correct mounting location for the ball stud bracket? Is the over center spring still in the car (on the clutch pedal)? As you probably know people remove it when they install a diaphragm clutch. Without it the pedal would not pull all the way back up and unload the linkage.
Just some rambling thoughts....
