@clinebarger - Looong story short, SUCCESS!!!
Assembled the rest of the transmission, triple-checking everything (
https://www.youtube.com/@transmissionbench7842 is a terrific resource).
As far as I can tell, we made two mistakes, both kinda-sorta understandable (I know, I'm rationalizing...)
Mistake #1: When assembling the pump, we got the sealing ring and o-ring reversed. My son said it's because the book says to "install the slide seal ring and rubber support ring into the slide groove", and we did it in literally that order. I'm betting that this resulted in less than wonderful pump performance, which caused the 3-4 clutches and band to slip.
Mistake #2: We installed one steel too many in the Low-Reverse clutch pack. My thinking here is that we mistook one of the original steels for a spacer plate. This caused the clutch pack to run hot, which scorched it.
Everything else in the transmission looked and checked out within specs.
But wait, there's more, lol.
After reassembling and reinstalled the trans, we hooked up the Quick4 controller, and it started acting up - clicking solenoids, freezing screens, etc. So we triple checked the wiring, the solenoid resistances, etc, no joy. Contacted the guys at
https://www.usshift.com, they said send it back and they'd check it out. They couldn't replicate any troubles with the controller, but still sent us a new one as a courtesy - and it works GREAT! I have no idea what was up with the first one, it worked fine while the first rebuild ate itself...
At any rate, all is well now, the transmission works like a champ, and we're slowly adjusting the shift points and firmness. Cool thing about the Quick4 is that it will allow 4 different "tunes", like "Normal", "Towing", "Valet" (never shifts above 2nd), etc.
Been a long drawn-out project, but I'm still glad we did it ourselves - my son and I both learned a lot, and had a (mostly) good time doing it.