Here is a list of changes between the 70mm Empire Strikes Back and the 35mm version (which is the one we all know).
* After the probot lands on Hoth and moves frame left, there is an optical wipe to the overhead shot of Luke on his tauntaun, instead of a straight cut.
* After Luke wanders through the snow and falls face down, there is an optical wipe to Han instead of a straight cut.
* The bacta tank scene starts on a close-up of Two-One-Bee and pans right to a closeup of Luke in the tank. It then cuts to FX-7 extending it's arm to the tank. There is no cut to Leia, Han and Threepio observing.
* In the snow battle scene, when Luke drops into the snow after throwing a charge into the Imperial walker, the AT-ST in the background has no atmospheric depth. It looks to close and small.
* In the Emperor scene, the hologram of the Emperor is already present in the first shot-it does not "tune in" gradually.
* The Imperial fleet establishing shot after the magic tree scene has a different TIE fighter sound effect.
* When Luke falls from Cloud City into the Millennium Falcon, the Falcon's radar dish is not added to the shot.
* The telepathy between Luke and Vader during the "Hyperspace" cue has straight cuts instead of quick dissolves.
* In the final scene, there is no tracked music from "Yoda and the Force". The scene begins with the first establishing shot of the rebel fleet, then cuts inside the Falcon for Lando to say, "Luke, we're ready for take-off" (but a different take of this was used). After Luke says (voice over), "Good luck, Lando" the scene cuts to inside the rebel cruiser where Luke says, "I'll meet you at the rendezvous, " etc. Not in this version are two more establishing shots of the fleet and an interim effects shot over which Lando says, "When we find Jabba the Hutt and that bounty hunter we'll contact you."
That list can be found in Volume 2, Issue 1 of Film Score Monthly. It was compiled by Michael Matessino who reportedly saw the film 70 times theatrically in 1980.
Neil