For those that might be interested, this is the story behind the alternate mix from Ben Burtt. I asked him about it in person around 20 years ago after I heard the alternate mix at a 16mm screening.
The mix was intended to be the final mix and was also intended to be presented in the Vistasonic format (that's a whole other story). But Lucas went in at the last minute and heavily cut down the opening of the ark scene. The sequence already had completed effects and musical score, but he felt that it needed to move faster. So he removed some shots and cut many others to be very short, particularly the ghost effects. That's why the music for the scene is heavily edited in the final film. If you are interested in hearing the complete scene, you can hear in on the Movie on Record which was released in 1981. That record also has other alternate bits of music, dialogue and sound effects.
Here's the ark opening scene:
Since the ark opening scene was re-edited so late in the schedule, the sound was hastily re-edited to match the new cut. This resulted in some sloppy music and sound effects editing. Time was short, so that mix was used to create stems for foreign language mixes and mixes for some Super 8mm and 16mm prints.
However, once John Williams saw how they had butchered his music in the ark opening scene, he asked for a remix so they could edit the music more to his liking. It was also decided at the last minute not to use the Vistasonic process and go with Dolby instead. So Ben Burtt took the opportunity to revise the entire mix, resulting in the more polished mix we are familiar with.
That new mix was completed very close to release, so it was only used on prints for the English release. The foreign dubs all used the music and sound effects stems from the earlier mix. You can hear some of those mixes on the DVD and blu-ray. You won't hear the alternate dialogue of course, but you can hear the alternate sound effects and music edits. Compare the ark opening scene in particular to hear huge differences in music editing, sound effects, even different screams.
It seems that the earlier mix is the only one which has stems available (for dialogue, music and sound effects). So that mix was used for the making of specials on the DVD and Blu-ray, and was also used for the recent orchestral screenings (because they only needed the dialogue and sound effects tracks). However, the orchestra plays the music as it was edited in the final English sound mix, not the alternate mix.
I have a Super 8mm print of Raiders with the alternate soundtrack if anyone is interested. It is 16 minute cut down version. There are also some 16mm prints out there with the alternate mix. And supposedly TBS once showed the movie with the alternate mix, but I have never been able to verify that.
Incidentally, the original 35mm 4 track mix has never been released on home video. All home video versions have used remixes, some derived from the 70mm 6 track mix.