Rebel/Nighthawk interchangeability

I'm curious if anyone can give me a definitive answer on whether or not the rebel 250 head will work on a Nighthawk 250 engine? Everything I have read says that the two engines are the same, except for slightly different timing and intake/exhaust (not positive on that one though). Both use the same Clymer manual, and are the same cc's if that helps. Thanks!