Would it be possible (/easy) to just integrate the dialog changes, hairy_hen?
This is actually the hardest part, for two reasons. The first is that the only source for the alternate lines is the mono mix itself; and given that it is, well, mono, it has everything else mixed in with it as well. Getting relatively clean copies of the dialog out of that might be possible—the Spectral Repair tool in iZotope RX 3 is really amazing, though this isn't really what it was designed for and it would be tedious and difficult at best.
The second reason is that the only mix of the film with the dialog confined entirely to the center channel is the DVD/Bluray version. Obviously when it comes to upmixing stereo tracks as I have done, there will be crosstalk between channels, and thus removing dialog to replace it with something else doesn't work. But when I investigated a while ago, I discovered that even the discrete 5.1 of the 1997 mix has some overlap of the dialog into the L and R channels, which means it was that way on the original 4-track master it was sourced from. Thus in either method clean replacement of the dialog is pretty much out of the question without resorting to the terrible later remix for those sections, or trying to somehow remake them from scratch.
Because of this, any such thing would have to focus primarily on including sound effects from the mono mix, rather than dialog.
The stereo foreign music and effects track has most of the changes.
What track is this?