Will the XR400 Head Gasket fit on the 400EX no problem or do they not match up. I dont know just how exact those two engines are. Thanks a ton in advance.

 

I think the XR400 and 400EX motors are one and the same except for the cam and transmission. The XR400's part # 12251-MBV-003 (head gasket). Why don't you chage the piston as well to a standard bore with a 10:1 ratio and the XR gasket and still run pump gas but with a bigger bang. I did it to mine and really enjoy the power change. Match port the intake and exhaust it will help.