Here's an update now that the engine is out.
The release fork is not broken.
After getting things apart what I have found is that the fork has not failed, but it appears that the pressure plate is too far extended into the bell housing.
This causes the "initial angle" of the fork when on the t/o bearing to be insufficient, so in effect the arc of the shaft rotation is starting too late and running out of room in the bell housing with the pedal on the floor (no board or pedal stop in place).
I had described a "nicking" sound. That is the diaphragm tabs contacting the fork shaft bosses, shaving bits of aluminum off.
My steel flywheel and AL adapter are from Renegade Hybrids, the pressure plate is from Kennedy engineering. (don't ask why, this has been muddling forward off and on for 10 years and started with a box of stuff picked up in a trade, I can't remember the basis for past choices) The crankshaft is 1966 Chevrolet, small journal 327, if that were to matter. Maybe the flanges were thicker than later ones?
I measured 66.5mm from the bell-housing
mating surface of the RH adapter to the outermost edge of the aluminum part of the pressure plate.
So with that background, I need to find out the correct distances are between components, and which component(s) would be best to remove material from.