The long plates are getting harder to find, you can probably still have the old one rebuilt. Is the current clutch a center Force? A lot of times it's the adjustment, they go over center and give the problem you describe. I know for the McLeod diaphragm I think the instruction sheet said something like 1/4 inch between the pp and the throw out bearing with the pedal up. I'd check that, loosen it up and try again.