Thanks guys, I got abit confused with the triple and twins section, anyway I know where to be now!

Im in Yorkshire by the way.
The main thing I'm short of is the engine! That was the main reason for finding a forum and to get help with getting it going. Apart from ebay which has a few coming up now and again where could I source a unit engine? My other halfs dad has a '78 750 Tiger, but apart from that I've zero knowledge of these engines. Is the 350 and 500 essentially the same? At the moment I'll consider whichever comes along unless someone persuades me one is better than the other. In the Ducati frame it will be quite a light bike, so the difference in displacement isn’t everything. What about tuning/fancy parts. The main firm Ive found for spares in the UK is supreme motrcycles but they seem to only stock parts for rebuilding?
I'll get some pictures up when the project gets more underway, and the moment its just a bare frame, I dont even have swinging arm yet but I'll be picking one up in two weeks! I race a single cyl Ducati and basically this is putting parts off the floor together into a bike, Seemed a good idea so we will see!