There is a wire sping type clip that hooks into the holes on the side of the clutch fork and attaches to the pivot from under the fork also, it is an Anti-rattle clip. It is a universal part to many of the Ford manual Transmission setups from the 60's-70's before the introduction of the cable actuated clutches found in the 5.0 Mustang. Check the surface of the fork that stradles the input shaft and contacts the throw out bearing under the riveted clips, the face of the fork should be smooth so it does not attempt to force the bearing sideways (which it cannot do) while bottoming on the clips on the bearing assembly as it moves through its range of motion, put a small amount of grease on the fork ends where they contact the bearing and on the lever pivot where it contacts the lever itself. I think these clips are universal, but check with Dave Kee or similar authority. The clip on the rusty lever is intended to slip in the rectangular slot of the Pivot that you are illustrating, it accomplishes the same thing. You may have a mismatched pivot and lever?
Good luck
http://www.scottdrake.net/prod_detai...Clutch+related