I think Yuseall (sp) was doing a sand quad (raptor I think) with a Honda RR motor in it. I've put a CB500 motor on a gokart before. Wicked fast, and it felt even faster considering your tush was only 5-6 inches above the ground.
You look at any junkyards? Sometimes places have a good assortment of bikes that work, but the front ends are smashed up and stuff due to hitting things like deer.
2008 700xx; Power Bomb header with power core 4 exhaust, Power Programmer III, pro armor nerfs, prm products control front and rear bumpers and full skid, 10" ITP rears, ITP Baja's fronts, RZR 2's all the way around, Uni filter, 13t sprocket, CCP steering Damper, DS450 shock swap, Dual Gasser Throttle, bar risers and Moose barkBusters. 730XX kit plus other engine mods!