I want to put a bigger engine in a 300sx. I have a couple of js550 piston port engines i could build up and put in but i am thinking about something like a 750 or a 650 neither of witch i have but i could get off of ebay. The issues i am seeing right now are the motor plate, the drive shaft, gas tank, water box, and cdi box. I have only had Js models. They are so simple and parts interchange so easily. but the sx is so different. Has any one out there done this?