I don't actually have the comparison track, because I've had trouble with newsgroup access, but I did download the in-theatre recording of the 70mm mix around that time. Sadly, I no longer have it, for it was a casualty of my old computer's death. The sound quality wasn't that great and the speed was too slow, but I do remember that most of it sounded very similar to the Definitive Collection mix. I've been making my replacements based on the list Belbecus provided, which I have saved to a text file.
There's one thing on the list that is confusing me a bit--he lists "water noise" during the garbage pit scene, but I've listened to it several times and for the life of me I can't find any extra water sounds that aren't in the 35. I think there are more splashes in the mono mix, but I have yet to find them in the '93. Just to be safe I used the older mix during that section in case there's something I'm missing, but I'm not sure. I know there are a few sounds that appear in the 70mm that weren't in the 35, but as yet I haven't found anything in the 35 that wouldn't also be in the 70!
As far as dynamics go, I've noticed that in the loudest passages on the DC, the very highest peaks are occasionally clipped. I'm not 100% sure if it is like that on the laserdisc itself or if that is an artefact of the sample rate conversion to 48 khz; but since Belbecus used a very high quality converter I imagine it is probably inherent to the source. It isn't really audible, since it doesn't ever clip for more than 60 samples or so, but it's interesting. Based on that, I would speculate that the 70mm original probably had additional headroom beyond what appears on the DC mix. Certainly its bass response would have been greater with two LFE channels--the '93 version could include only as much low frequency information as two channel dynamics will allow for. I recall the in-theatre recording sometimes showing peak distortion, often coinciding with LFE from the special edition. Exactly how loud the bass actually was is unclear, and will be the aspect of this recreation that is most subject to my creative judgement.
I only have the '85 mix as a lossy version from the Editdroid disc, but aside from a widening of the stereo image and the insertion of C-3PO's line about the tractor beam, it appears to be identical to the '77 stereo, including the dynamics. I too have noticed the music reverb you mention in the quad laser scene; it must have been a creative choice of some sort.
Since the 70mm mix featured surround sound, a 5.1 track would probably be the best way to release this, but certainly stereo or 2.1 versions can be made available if desired, as well.
I appreciate your encouragement! It's definitely closing in on completion . . .