The 70mm mix hasn't been officially released in its original form, but the 5.1 version included here is a close recreation of it, which I assembled using various laserdisc sources and a lot of very careful listening. While it doesn't sound exactly the same as the real thing, it is very close, and it would be pretty difficult to make a more accurate version without access to the actual master.

So in effect, the 5.1 mix can be considered to be the audio equivalent of the Despecialized Edition's video work. ;)