Here's my attempt at a repair. I'm actually somewhat surprised it went so well... I drilled a hole in some 1/8" steel that is the size of the ball amd made sure I could slip it over before attempting to weld fill. Then used my table sander and rotating motions on the primary axis to get it back to circular shape and verified by fitting the steel hole over it repeatedly. Then I started contouring the ball
Next I put it in the vice and started fine tuning with a file.
After my last photos I used finer sandpaper by hand and also pressed it I to the rounded retaining cup and kept attacking it unil there were no crunchy spots left as I rotated the cup around (without sandpaper).
So... I doubt it's perfectly in spec, but it is pretty darned close, and much closer than it was.