I'll admit, I got off the train at about 1975 and never got back on or moved forward. I think they call that Old School. Unless things have changed, back then there were 3 type pressure plates for a single disc chevy clutch. Diaphragm ( most common) and (2) 3 finger type, Borg&Beck and Long. Never knew what the origin of those were? Just accepted that fact. The 3 fingers were preferable for racing.
Back around 1981, I decide that my perfectly working Scheifer diaphragm plate (which was warped concave) needed replaced. I put in a B&B style plate with a new "Zoom" disc. Got it all sorted out and wanted to show this thing off to a buddy. We are at a light on a four lane and when it turns green, I drop the hammer. My car would put down some hellacious posi stripes usually 100 ft. Or more. This day it was hooking up good though. I come up to the next turn off and push on the clutch to down shift. Nothing! Still had pressure plate feel, but the car would not down shift. So I cram on the brakes harder and slow enough to come up to the lh turn lane. The car stalls! What the heck? I put her in neutral, start her up, and I cannot get it into any gear. I shut it off, put it in 1st ,start it in gear, and limp the thing home. I get the clutch torn down. My new Zoom disc has 3 spring steel paddles and that is it!! All the lining on both sides of the disc are completely shredded off! Gone! No lining. I can see toward the rear underside something fuzzy looking. Back on the rear axle housing, the 2 turbo mufflers and the underside lip of the tail panel is this shredded fine textured fiberglasss looking material that used to be my clutch lining. Now I know your car is not a big block, nor is it H.O., but it is possible, by what you describe, that something failed in that area ? You won't know till you tear it down. But this is why I say clutch. Good luck
