Like Coolhand said. The 05-06 900 (866 cc) and the 06 700 (755 cc) are the only engines that will bolt in to that chassis. If you have crazy mod skills, you may be able to fabricate a way to mount a different engine, but you will also need the electronics from the donor sled. The 900/700 is fuel injected and the electronics are all feeding the ECU for fuel/spark. So if you decide to tackle a transplant, make sure to get the wiring harness and electronics from the donor sled.