While reading about the front driveshaft flange on another thread, I went out to take a look at the 1650's flange. It's shot. I can remove the ball from the flange:
This is one of the parts that gets destroyed when your ISO mounts wear out, along with your flex discs. The 1450 has a new one that was put in this Spring by the PO at the dealer. Part cost was $40.