Well, it took a bit longer than planned, but the transmission and inner driveshaft are back together. There are three cover plates on the transmission: two on the right side (one of which houses the dipstick guide tube), and one at the back (which gives access to the differential). Each inner driveshaft has its own carrier, so in order to reseal the whole thing all you're looking at five different parts that have to come out, get cleaned, and reinstalled with new gaskets (in the case of the plates) or O-rings (in the case of the driveshaft carriers). It's not difficult, but it is tedious, and access to some bolts is not great, which means lots of stretching and twisting.
The plates were no real issue, but the right side inner driveshaft - the reason for this whole project, for reasons that will be apparent momentarily - was a bit uncooperative. Six bolts hold it in, after which it must be twisted out around the inconveniently-placed downpipe. I got it out OK, albeit after a bit of prying and mild swearing, and took it apart. The old inner seal did not want to leave, so I carefully cut most of the way through it with a Dremel, after which prying it out was easy. The new seal went in OK, but when I popped the new inner driver in the bearing (which was fine and is not being replaced) became unseated, meaning I couldn't get the retaining circlip on it. This was last night, and as I was already fairly tired, I left it for this morning.
The old driver had been damaged by a failed tripod bearing, caused by an apparent lack of lubrication. It was so dry in there I swear it was assembled without lubrication at some point. Each leg of the tripod bearing is supposed to run in a smooth channel with two smooth surfaces. When it fails one side of each channel starts to cup, leading to vibration on acceleration. You can see the failed tripod bearing in an earlier post, and here's what it did. The cupping is visible directly below the red line. It's bad.
Having thought about it last night, and confirming my suspicions with some online research, I headed out to Lowe's to find some sort of pipe I could use as a drift to reseat the bearing. For anyone who's in this situation, two 1" PVC couplers work perfectly. Stacked on the bearing and held in alignment by the driveshaft, a block of wood on top and a few shots with a hammer and the bearing sat down. Clip on, new outer O-ring seal in place, and it was back in the car without drama. Here is the assembled unit waiting to be reinstalled.
I have to say that my Milwaukee electric ratchet made this whole job so much more pleasant. Whoever it was on this forum who turned me on to this thing, thank you.
So now I'm just waiting for a new wheel bearing and I can button up the front end (new shocks will go in at the same time - the old ones had to be cut out). Then it's on to the rear and welding up the failed right side shock mount.