I researched Fantasound as well and I’m recreating the Fantasound sountrack by using two sources, the 1957 stereo LP soundtrack and the mono soundtrack. For the choir and soloist parts i also used the linear track (which also has the mono mix) on my PAL VHS of Fantasia.
Tried that years ago (even brought it up in the old editorial) and realizing the originally intended sound design is going to be a helluva lot more complicated than just sandwiching the LP and VHS audio together. Assuming you used optimal equipment to yield a clean capture, synchronizing a slightly faster or slower LP recording to marry perfectly to the timing of the animation is its own challenge, but then comes the issue of a narrowed sound field after slapping a monoraul downmix over the stereophonic recordings— a lot of the movement will be hard-centered and destroy the illusion of sound that’s supposed to follow the action on screen. No one particular soundtrack source— even the magnetic stereo tracks— will ever get you the sonic experience that Disney and Stokowski intended. Each come with their own set of problems that restrict them from meeting today’s exacting high-resolution audio standards. But to reveal exactly how one would go about bringing the best quality out of mag recordings (which themselves are only copies of a copy of recordings from the late 30s) would spoil the contents of the upcoming editorial. I can promise you this much: it’ll be well worth the wait.
Until then, you’re more than welcome to give it a shot anyway; this community embraces the exploration and research of various source material after all. But take it from me, you’ll be spinning your wheels with this one. Again, restoring Fantasound is all lot more complicated than you think.