morgands1 said:

The distant roar of the wampa (where we see his shadow lurking) matches on both 70mm and 35mm. If one then ties the music cue where Luke sinks back down after trying to free his frozen boots and then tries to reach for his light sabre, all that - and subsequent sounds - match.

So the extra 5+ seconds occur as Luke comes to and reaches up to find his feet frozen into the ice of the ceiling. The added shot is probably the closeup of him just before he reaches up towards his boots, as seen in the master shot.

I ran your version in sync with the '85, and that closeup does seem to be the extra bit of footage.

This is interesting, because that shot was also included in the 70mm film cells:

As I pointed out, there are also 70mm cells of the bacta tank wide shot.

This either means that there were 70mm prints made of the revised version later in the summer, or that the cells were taken from a newly struck print made specifically to be chopped up into these individual frames. (But if so, why would they have sound-striped the print?)