[Doug Zielke]

Blue,
I own a '96 900 SS SP, essentially the same bike but with a full fairing, and a few other bits.

Being only "Desmo due" (2-valve), they are not as complex as their Desmo quatro relatives. Just like Porsches, if there is a solid history of service, then you should have no fear.
Because the OHC's are *belt* driven, you should determine if the belts have been properly maintained. I replace mine every 2 years regardless of the mileage. The belts are not expensive, but tangled valves are.

As far as I know, there are no huge repair issues. These 2-valve motors have been around for a long time.

BTW: If you buy a 2-valver, let me know. I bought out a nice selection of factory tools from a defunct dealer. I have all the special tools you will need to do the valve adjust.