Why not just take a 990 motor and have a bunch of work done to it? It will handle much better in the chasis and have a better power curve for your type of riding. You can do a lot of stuff I would imagine. Porting and polishing the heads, valve job, forged internals with high compression pistons, balanced and blueprinted. Have a shop make a custom ecu tune for it and that would be a pretty beast motor.
2014 Yamaha Bolt