A while ago I started to do something like this myself, but didn't finish it for various reasons.
There are many, many differences in the mono mix that have never been pointed out before, and I'm sure there are ones that I haven't noticed, even with all my attention to detail in this kind of thing.
I can tell you right now that putting the mono mix in one channel and a fold-down of the stereo mix in the other won't give you a completely accurate comparison, because all the surround effects in the stereo mix will phase-cancel themselves out, and thus be inaudible. (And yeah, there are many more surround effects in there than just the noticeable ones, lots of ambience and things of that nature.) Virtually none of the sound effects that were put in the surround channel were included in the mono mix at all; therefore they'll be altogether absent from both channels of a comparison track and won't register either way. It just isn't so simple as that, I'm afraid.
The reason for their omission in the mono I'm not sure of, but I would guess that it was probably to reduce noise by having a lesser number of tracks mixed in, since the format was low fidelity and frequency-limited to begin with.