I would not be at all surprised if the 5.1 track was merely a cleaned up and newly EQ'd version of the old 5.1 done for the DVD. Probably pretty good, but lacking in the low end and ambiance of the original mix.

BTW, I've found that for many 80's action films that did have a 70mm blowup that the 4 channel mix was the same for both 35 and 70mm releases, minus of course discrete channels and the extra punch of baby booms, and on some occasions that the 35mm matrixed version sounds just as good if not better.