I think the answers are:
Swingarm is bound to be the same, Ducati are cheap like that. UK SSs have always run 180s on 5.5in rim (I had 180/70 Dragons on my '92 900).
I would also imagine the 900 and 1000 frames are near identical. I'm looking to drop a 1000ss engine in my superlight in the future, and so far have assumed it'll slot straight into the '96 frame.
If in doubt, contact the specs master:
http://www.geocities.com/edwyun/myears.html Cheers and good luck,
Ali