Well F.
I must have a clearance problem in the bottom because I can't get the output shaft to seat to the point where I can get the top snap ring on. I had the same exact problem on my trans, it ended up being a tabbed thrust washer that got out of alignment. I'm guessing the same thing is happening here, although it's a little more confusing. There are already 2 different clutch packs installed that fit behind snap rings that fit into grooves in the case. If there was a clearance issue I would've expected lots of trouble seating those snap rings, and/or out of spec clearances on the clutches, but I'm right on the money there. Since the snap ring grooves are in the case itself, they sort of set where everything behind them will be if that makes sense.
The other possibility is that the output shaft itself is getting hung up somewhere on the output support. It looks like it could go in another 1/8" but it just won't. It also would mean the speed sensor magnet thingy would maybe ride on the output support but there is no bearing there so it doesn't feel quite right. OF COURSE I don't have a picture of how that was seated before I tore it down.
So to tear it down the rest of the way involves getting off this MASSIVE snap ring that I spent another hour on last night before I called it for the night. So annoying. I can rebuild a trans (ostensibly) but I can't deal with a flipping snap ring. grrrrrr