get a small lawn mower battrey (WALMART) and run a crf 450 regulator with the 12 volt clone engine power, ditch the EL start and you can use a waYYYY smaller battrey, if space is a problem that is..

or just run the lights off the motor and you wont need a battrey at all, although you will have dim lights at idle

 

I have to have electric start because the motor sits too far in the frame to have a kicker. It shouldn't be too big of a deal. Big concern not is getting rim modified to take fiddy sprocket.