I googled ds650 performance.
Oh, and it is Can-Am ds650. (By bombardier)
These guys do piston kits, gaskets etc: http://www.ctracing.com/ds6501.htm
Ah, here is the 800cc kit. ( I was nearly right): http://www.omwracing.com/engines_rotaxds650.htm
You'd have to figure out the injection and timing. But would be a fun project.
There are plenty more to choose from . Might be a good place to look for gaskets.
Anyway, just FYI.