Okay, status update:

Video and English mono audio: DONE. I had to trim a few frames at the scene transition to get audio sync just perfect, but the audio splices in absolutely seamlessly, no adjustments other than volume required, and it's exactly how I remember it now! I'm coming up on a busy week so I may not be able to show a clip for a while, but it's in the bag.

I am currently experimenting with trying to port over the Blu Ray commentary tracks (basically I just need to cover the splice, and remove things like "and here we restored a scene that had originally been cu--"). And maybe I'll try to port over the subtitles, similarly just covering the transition gracefully while probably losing a line of dialog at the transition, which actually isn't a very big deal at this point in the scene.

For foreign dubs, if you want one, you'll have to send it my way. All I have is the Blu Ray dubs, which appear to be based on the new mix (actually I think the commentaries are stereo-downmixed from the new mix but I'm not as concerned with that--can anyone verify this anyway?). No guarantees that sync with other languages will be as easy/possible as with the English, but I'm willing to try, and I suppose I'll have a little more wiggle room because I won't have to match lip movements...

EDIT: Dang, that was fast. Both commentaries converted over, so that's what I'll use unless I can use sources based on the mono mix (right now, it just sounds like people stop commenting for a few seconds during the transition and then they continue as before--the soundtrack is still quietly playing the whole time). Now it's just subtitles and foreign dubs!