Ive just bought a yz400 with a 426 engine as a second bike to my wr450 and was wondering if the 400 head will fit onto the 426. i bought this bike as a project knowing the engine was blown up. i also got the original 400 engine with the bike. the 426 has droped a valve damaging the piston and head. so if possible i want to fit the 400 head onto the 426 with new piston and conrod and big end bearings.if this works i will end up with a cheap bike. considering i paid only 1000 dollars for the bike with 2 engines. if anyone could answer this question it would b greatly appreciated.