I have an 08 exhaust on my 03 650, that should be the same as an 02? It fits but i had to make up a little bracket as the point where it bolts to the frame is slightly different, and the silencer brackets are different and needed a spacer and longer bolt on the rear mount. Very easy though, so no problem.
Others may be able to give you a better idea on power differences. I cant say i noticed much difference to be honest