It is the type of levers inside the shift cover on the trans that operates the shift forks in the transmission.
There is two types mopar made, and they changed around 1970 but either one will work.
My guess is you have a POS pressure plate, or the disk itself is warped really bad.
Went thru the same thing a couple years ago.
Bought a Zoom MU series clutch, it would grind and not go in any gear.
The techs at Zoom finally after several conversations said to send it back for a refund.