Interesting. I've seen RMS measurement suggested elsewhere as an indication for setting Dialnorm, but I don't really know that much about the specifics. Commercial dvd's are all over the place with this sort of thing too--I think a lot of them just reduce everything by 4 db without measuring, which is especially irritating if the material is already encoded at a lower level to begin with. The GOUT audio has certainly been subjected to this, which is the main reason it seems anemic compared to the laserdiscs. Dialnorm can be a useful device, which Dolby had good intentions in producing, but unfortunately it is too often misunderstood and misused in the real world. An example their documentation provides is reducing the volume of commercials so they don't sound blaringly loud compared to programs with lower averages, but I don't think it has ever actually been used for this purpose!
When combining segments of the '77 stereo mix with the '93, adjustment was required nearly every time to get them to blend. I used Belbucus' level-matched version, which plays at a similar volume to the '93, but even that was not identical because of the differences in dynamic range. Most of the time reducing the '77 mix by 1 db provided the best results, but sometimes even if the dialogue came into alignment the background sounds wouldn't be the same. Louder sections were raised anywhere from 2 to 4 db to try to compensate for the dynamic shortcomings, but while the results are certainly listenable, the more powerful original can obviously not be recreated. Strangely, one especially quiet moment had to be raised 6 db in order to fit. This was done from looking at the waveforms, with further fine-tuning by ear as needed.
You'll never get an exact level match between the various mixes. Dialnorm can certainly help to even them out, but it's only an approximation. Still, as long as the averages are in the same general area, that's what matters.
I do think the 70mm mix probably had more dynamic range than its '93 downmix, owing to having multiple discrete channels, and evidenced by the occasional brief clipping of the '93. 16-bit pcm has a pretty good range, but sometimes it does fall a bit short of what is needed to convey sound without compromise. Present day 5.1 tracks have dynamic potential more akin to a 20 bit range, I believe.