Two bits of good news:
1) A kind forum member (who shall remain anonymous, just in case) has pointed me to a torrent of the DVD-9 PAL Revisitations version, and it's downloading quite quickly!
2) I seem to have had good success in the following with the DVD-5:
- Cinema Tools is able to convert the PAL video and main audio to 23.976fps NTSC just fine. A couple of shot transitions have blended frames, but I notice no jerky motion, and frankly, I'm not that worried about it being 100% perfect. At least I know it's possible now.
- I'm working with Soundtrack Pro to adjust the audio of the commentaries while preserving the pitch. I'll update about this later when I know more about how this will pan out.
So, I just need a way to adjust chapter times and subtitles from PAL to NTSC, then I'm golden. I'm going to leave everything else on the R1 DVD9 alone, so just the main movie (video, main audio, both commentaries, isolated score, both subtitle tracks, and chapter timings) will be altered compared to the retail disc.
I'm not quite sure how I'm going to do that yet, but I'll figure it out...I hope.
--edit--
I quite like the results CinemaTools has provided. It may not be perfect, but damn it, it's more than good enough for me. I might fine-tune it a bit more once I finish downloading the DVD-9, but I may not. I haven't noticed any issues in effects scenes - titles and credits look a little wonky, but they do in the PAL version, too, so I don't see that as a problem.
I've also had some success in time stretching in Sountrack Pro without affecting pitch, but I can't quite get the sync to work for some reason. I'll figure it out eventually, though.