I have the original Xanadu disc, and am pretty sure it's anamorphic.
One review of the early letterboxed Tron DVD from Disney claimed it had a 4.1 mix, but that may be a typo?
Grease got a dreadful remix for the 20th anniversary, and has stunk up every video release since then. As detailed earlier in this thread, I successfully captured Grease's original mix from VHS hi-fi a while back, but haven't found anyone to do something with it.