Sooo... after a lot of back and forth at this machine shop and that transmission shop and blah blah blah we put it back together...
Put the torque converter and transmission together as a unit to install it all together, after getting a lot of votes, especially from the local professionals. Actually, only my first original mechanic was the one in favor of installing them separately, and that's very likely how it got damaged in the first place.
Worked the thing pretty hard for the last few days and it appears to be functioning properly. Full wheel spinning power, and the reverser oil never gets really hot. Hope it stays fixed!
Thanks everybody for weighing in!