It looks dry in there, at least best I can tell. But it sure sounds like how a contaminated disc behaves. Anything coming from above, like from the oil sender area?

Maybe somebody could give you dimensions from a correct z bar and weld up something from the pile?

Nothing wrong with a diaphragm clutch, other than installer error and lack of driving skill. I won’t use anything but a diaphragm and centerforce has always worked well for me. You checked off the big no no, the over center spring. So it had that in there for both clutches. Plus a linkage mess, plus the slick flywheel, plus we don’t know how any of those involved broke it in. I think at this point I’d solve the linkage issues and go with all new parts and do as much break in as you can yourself. With the spring out of the dash it should end this ordeal.