I'm in the process of doing several things to the '69 at once...trying to figure out the rough idle issue (just bought a supposedly good used distributor on Ebay to swap and further narrow the problem), continuing to work on the dash pad and heater box (the box's movable flap is stiff from sitting for 39 years...it's slowly getting loose again with a dab of lubricant and working it), and the chattering clutch issue. My buddy Scott and I dropped the tranny last night and put eyes on the clutch and pressure plate. The clutch disk and PP are original GM parts and had probably never been out of the car. The disk was approximately halfway worn down...still plenty of miles left in it, and the PP was very shiny, just like a mirror. There is probably less than .010" of wear on the PP, but I'm dropping it off at NAPA today to get resurfaced. The mirror smoothness of the PP explains why the clutch chattered...it was hard for the disk to grab onto. I'm replacing the clutch, PP, and throwout bearing to get the car back to peak drivability. Still looking for a 3-on-the-tree column (in case anyone on here knows of one).