An update:
The primary recommendations I got were for Midnight Motorsport and Vintage Racing. I talked for a while with Byron Sanborn at Vintsge Racing. It’s clear that they know these cars, they know the transmissions, and he and I traded some notes on my current situation. Based on the condition of the transmission (it looks quite good externally, has been checked by the seller before shipping it to me, etc) as well as the potential cost for a tear down ($500-800 depending), he basically echoed Pete in saying “I think I would just put it in as is. It’s not leaking, it’s coming from a reliable source, and if you have an issue, you clearly know how to remove it and at that point spending the money will be worth it to you”. In their estimation the likelihood of that coming to pass would be low.
I do think that Don is correct, especially from a guy in his situation - if one of us is paying him to perform a rebuild, it’s on him to ensure that the car he delivers is rock-solid. I’m willing to have something that is 95% chance good and 5% chance I’m back in a year changing out the transmission, and in the meantime use that money for other things on the car.
But wanted to follow-up since based on my discussions I could endorse either of these places as somewhere to take your car in Seattle.
I should add as another option that when checking out an MG for a friend being advertised on BaT, I had gone to the Shop - it’s a high-end car storage place/restuarant/hangout etc - since the car was being stored there. They have one in Houston and one in Dallas. A little bit of a gimmick, store your rarity amongst all the others and can work on it there, etc, but sure, it’s neat to check out and if you can afford to store your car there it’s beautiful. BUT, while there I had spoken with master mechanic Guy who was actively working on a beautiful 1968 BMW 1600GT. It was clear that he knows his stuff. Even non-members can get service there, but I don’t know if it’s much more expensive than other options. But one to consider.