[Christ]

I think I'd use the rotary throttle control from the motorcycle...

Also, a slightly lower seating arrangement would benefit the rider and the aero alike.

If it's rated for high speed use (it has street tires... so why not?) a slightly longer rake on the front end (more caster angle) might help to stabilize it from the front end shimmy that Quads tend to have at speed.

I absolutely must see more of this project. I planned on doing something like this awhile back, but never made it out from the planning stages.