I think slob's right about the cams.
I have this page bookmarked from Brad the Bike Boy - note 3 suggests that the cams should fit:
http://www.bikeboy.org/duccamspec.html
"Not all cams are interchangeable.* The 1000 DS (and now 696 and 796) cams are unique, running in the head itself without ball bearings.* The 620/800 cams run in ball bearings like the earlier cams, but have two supporting bearings instead of three, and the location of these is different to the earlier cams.* You could make them fit if you really wanted to.* All others are physically interchangeable."