With all due resect to the OP, I’d take that post with a grain of salt; I’ve worked extensively with the same vinyl recordings for a very long time, and once you adjust the timing (vinyls always tend to run either infinitesimally slower or faster than the master source depending on what player is used) they lock to the picture perfectly because they are, in fact, not outtakes. On both the 35mm mag tracks and vinyl/reel tapes releases, one particular incidental string noise heard on the left channel in the Toccata segment, as well as panning and discrete channel dropout across all segments, are identical to one another in both sources. Take my word for it, these are not outtakes. The surviving recordings on film and commercial audio releases are one and the same. That is all that has survived. Any actual outtakes would’ve been on the raw, unedited recordings sessions on the original nitrate film sources which, sadly, no longer exist.
The monaural downmix prepared for the wider 1941 RKO reissue was the basis for the subsequent mono pressings on commercial audio and the 1990 VHS/LaserDisc releases. Having personally studied the mixes just as carefully as I have the stereophonic recordings, I noticed identical instrumental prioritization across all releases (which itself can likely be attributed to an entirely new mix that sourced the original stems when they still existed).
Short of having access to a magnetic stereo copy of the 1956, 1963, or 1969 releases, the stereophonic vinyl and reel tape releases are technically the closest you can get to the “original” Fantasound, but not without its own warts. The original stereo tracks had zero reverberations baked into the final mix-- dry as a bone all the way through, and that’s exactly how it sounds on the surviving recordings used in the mag stereo prints. So the reverberations weren’t “removed” in the 1990 reissue-- they were never there in the first place. So, while the dynamic effect of hearing the score play in a concert hall does make the commercial pressings a worthwhile listen (I can’t count how many times I’ve enjoyed them), it’s ultimately an artificial effect, and the release still has the issue of a faint phantom centre channel that needs to be adjusted for proper listening, as well as occasional hard pans that aren’t nearly are strong as they are on the mag tracks.
TL:DR: the stereo and mono reel/vinyl pressings are totally listenable, but the optical mono and, especially, the mag stereo tracks will get you the closest to the original sound elements.