This article just popped up showing off a guys 500cc triple that he made a frame for. The suspension is from a ZX-9 and he was very smart to gear the bike for acceleration and a decent 120mph top speed. The shocker is that it weighs just 310lbs. Now that would be a fun bike to try out.
Have a look at Jays 500 - why do they call it the XJ500T? You got me on that one...