They're model specific to a large extent. Actually "engine family" specific. YZ/WR400/426 can be interchanged as whole or partial sets to some degree. The '03-'05 YZ450 is a 4 speed, but can be swapped with '03-'06 WR450's as a complete transmission, including forks and cam. Later 450's can be swapped or partly mixed, but that won't help you.