Looks good Skids.
The only thing with sound of thunder is that an air-cooled two-valve machine is not even remotely in the same league as one of the 4-valve RS's or similar that seem to be all over the place. In Thunderbikes the 1000DS engine would be competitive, the rest is down to the rider.
Your 750 idea has merit though Kev, it's a cheap way of getting a half decent bike into minitwins. I think that it's pretty much the same sort of bhp numbers with maybe slightly more torque than a well setup 620 though. Not that I've just been researching this
Have you checked out the ECU yet? Can you change the maps in the standard ECU so you can run open cans and some tuning?