OK, more info on the home video releases of The Big Trail.
The initial US home video release of the film in 1988 has a sleeve that says 110 minutes and the VHS itself says approximately 112 minutes. The catalog number is 1362 and the UPC is 086162136238. Being early Fox, it's presented by their Michigan-based subsidiary, Key Video.
The film ends up to be 121m:28s including exit music. It's the same print as the 1990 UK VHS release (which has the same catalog number) but has subtitles for sections where the audio can't be heard. The exit music doesn't appear on the UK VHS either. Confusing, huh? It looks like the audio was restored in the two years in between.
So these early VHS releases are the same as the Fox Movie Channel print except not widescreen. The FMC print doesn't have exit music to my knowledge (at least not my copy).
The 1988 US VHS was repackaged with new cover art in 1993 and retained the same catalog and UPC numbers. I don't know what's actually on that edition, though, nor the final VHS incarnation that has a different cover and catalog/UPC number. In any case, I wouldn't believe the running time printed on the jacket or tape.
The first UK DVD of the film has a catalog number of 1362DVD, but it has been confirmed to be the standard 108-minute version released on DVD worldwide.
I've been told that the really long version of The Big Trail was never released theatrically, that the film premiered in Grandeur at 125 minutes. So what's missing compared to the FMC and early VHS prints would only be a few minutes. Evidently this remaining footage still exists but is in rough shape, especially the soundtrack.