To the best of my knowledge I believe the clutch pedal arm and pivot shaft itself is the same from 60-66. I’m pretty sure the clutch arm in my truck is from a 63-66. I picked up the complete mechanical linkage setup to install in my 1960 when I swapped from a TH350 to a Richmond 4 speed. The only difference I’m aware of is the lever arm that clamps on the passenger side splined end of the pivot shaft. The arm for the mechanical linkage is longer and has a different shape. I changed my mind and went hydraulic instead, and installed the later clutch arm when I discovered the original 1960 version was loose on the pivot shaft.
Post #2 on the attached thread shows how I did mine:
http://67-72chevytrucks.com/vboard/showthread.php?t=440979&highlight=hydraulic+clutch
