OK, I'll give my 2cents on the trans oil discussion. IMO it all depends on the condition or the synchronizers themselves. Good, tight, little wear, good grooves in the contacting faces, those would get ATF in my trans. More wear, may require something closer to the original.
I base this on the factory recommendation from around the mid 60s. The A833 in my 65 Dart came with Type A from the factory, as did most. There where a few complaints of a gear rattle in neutral from some owners so Mopar suggested a change to 80w90 for those only.
That little Dart was the best shifting standard trans I've ever driven. That's why the one waiting to go in my 56 pickup already has ATF in it.