I read something in an earlier thread, and now even a search won't dig it up for me. I remember something about the valve reliefs on the 250R piston changing at a certain year model. (I know about the valve stem diameter change in 08) I know that everyone says to use an 08 R piston for 13.1 comp. Will this piston work with both an 07 R head and an 04 X head? My 04 is due for a rebuild. I intend to buy an 07 R head and install the R piston, but would like to rebuild the X head also, so that I always have a spare to just bolt on. Will these two heads both work fine with the 08 R piston?