Here's what my handy dandy 68 shop manual says:
1. disconnect the clutch return spring from the release lever.
2. loosen the release lever rod lock nut and adjusting nut
3. move the clutch release lever rearward until the release bearing lightly contacts the clutch pressure plate release fingers.
4. adjust the adapter length until the adapter seats in the release lever pocket.
5. insert a feeler gauge (0.136 for all except 390 engines; 0.0178 for 390 engines) against the face of the rod adapter. Then, tighted the adjusting nut (finger tight) against the gauge.
6. tighten the lock nut against the adjusting nut, being careful not to disturb the adjustment. Torque the locknut to specification.
7. remove the feeler guage.
8. install the clutch return spring.
9. check the free travel at the pedal for conformance to specification. readjust if necessary.
10. as a final check, measure the pedal free travel with the transmission in neutral and the engine at about 3000 rpm. If the free travel at this speed is not a minimum of 1/2 inch, readjust the clutch pedal free travel. Otherwise, the release fingers may contact the release bearing continuously, resulting in premature bearing and clutch failure. Free travel must be exactly to specification.
clutch pedal free travel (engine running) 3/4" - 1 1/8".
clutch pedal fee travel adjustment nut 17-25 ft-lbs.