Right, found a major change in reel two:

After the “mind block” scene, when THX is taken away, we see him on the floor with a bloodied back and the guards are tying his hands… The two differ after this:

On the LD, it cuts to his trial and then in the white room surrounded by guards with sticks. Then he’s on the operating table getting his “surgery”. Then cuts to him on the floor convulsing and there are two men talking over a TV image of him convulsing. He wakes up, LUH runs to him, they make love. They are then surrounded by guards.
On the 35mm sample, it cuts to him in the big white room on the floor and LUH runs to him. They make love and are surrounded by the guards. Then there’s THX getting his “surgery”. Then the trial scene. Then THX is sitting on the floor in the white room and is surrounded by guards with sticks.

Unless it’s on another reel, the scene with THX in convulsions while the two men talk is missing from this 35mm cut.

EDIT: Just watched the 1971 16mm clip at this point and it’s exactly in the same order as this 35mm sample. So, this Italian cut is pretty much the 1971 cut with inserted Italian computer information screens and credits and a missing shot after the credits and at the end of reel 1.