Well, the negative doesn't have any soundtrack attached to it. The mix would have been recorded onto reels of multitrack tape running in synch with the picture (not the actual negative but a copy, to reduce physical wear and tear), which were then put through further processing and duped onto printmasters for each film format the movie was due to be released in. The 4-track most likely exists as audio only, without any actual film being attached to it.

As a point of interest, the 4-track was also the main source for the 1997 Special Edition mix. If you listen to any part of the movie that hasn't been re-edited or had additional sound effects piled on top of it, you can hear that it is extremely similar to the 35mm stereo and 70mm versions. Because of this, it makes for a much better listening experience than the DVD or Bluray (which are outright terrible).