dont waste your time. most street bike motors are way too tall for the banshee frame. you would need a raptor or yfz450 frame.
also, the added weight on the motors really slows them down in atv frames. they need to be running hard and producing some big numbers to make it worth it.
do yourself a favor and just mod your banshee. it will be lighter, easier to handle and easier to work on.
ive done several conversion bikes. they are time consuming, expensive as fuck and harder to make work right.