This is the third time. Anyone else have this happen. I will be out riding and get lazy and shift with the back of my heal and maybe i'm pulling to hard but the little ball on the end of the shifter is popping out of the pawl in the trans. When this happens I've been stuck in 1st (two times) or 3rd (most recent) gear. Have to pull the whole trans out to reinstall. PIA
I have taken a straight edge across the mating surface of the trap door and measured with calipers to the ball at end of shifter and then from the face of the trap door to where the shifter ball engages the pawl carrier assembly and they are spot on.
Clueless??? Could the pawl carrier springs be weak?

 

More likely the ball is loose just from wear. Or there is a thrust washer missing. Or shim it tighter.

But, I would also take a close look at the entire assembly.

thrust washer pn: 34060-52 for your '73