It lives! It lives!
After three months, I now have a working Model F XT. I haven't done much typing on it, but Aqua's Key Test shows each key registering just fine. Miscellaneous comments about things I encountered that weren't highlighted enough:
* Clamps! In this case, the clamps are used to compress all the parts so you can turn the mounting plate, foam, barrel plate, and spring sandwich on its side and give the back plate a couple whacks to get everything together properly. Learning this saved me easily two hours. I used some bulk plastic clamps from Amazon I had lying around and, while the clamps did fly off across the room, that sandwich came together in two minutes or less.
* Foam! First, do yourself a favor and download the template from Snufkin's post.
For me, I had to use the innermost rectangle, i.e. the one that looks like it has tabs. The old foam mat shrank to about 3/4 the size of this template, which was the main reason I was begging folks to send me some foam. Note that the holes are perfect for a 12mm punch ... which I'd link to if Amazon still had it. Most hole punch sets don't have a 12mm.
I did end up using 2mm foam. I think that's probably a bit too thick, but 1mm was too thin, and 1.5mm was impossible to find in small quantity or it was too large enough/too small, or was backordered.
* Grounding! There's a grounding cable off the keyboard cable. It's supposed to connect to one of the screws. If you don't have the keyboard properly grounded, you'll get random text and other badness.
I did have to disassemble three or four times because of keys not registering right and/or bent springs.
I ended up buying all new springs, flippers, and 26 barrels. I have a BUNCH of extra parts that I'll sell. I also need to decide if I want to keep this keyboard.