I've got a 07 wr450 and I want to build a spare motor for it . I know where I can get a 06 yz450 motor with no head on it . I know all the gears in the tranny are differant and the left side of the crank shaft , stator and stator cover is also differant . but I was looking at a parts book and noticed that the wr and the yz have differant main case part #s . Does anybody know what is differant at the main case ? can I use a Yz one?