If it's the same as an H, it's simple enough to check out.
The PTO shaft inserts into a socket in the innards of the driveline, with a sleeve around the shaft that slides into some lugs into the driving gear. Just park the tractor with the front end lower so gear oil doesn't run out, remove the bolts, and pull the PTO assembly out. It helps to slip a piece of pipe over the outer shaft for more leverage when pulling it, 'cause the unit is "front heavy".
I never had the lugs go kaput, but I did have a shift sleeve break so it wouldn't shift.