i got a few interchangability(is that a word), questions. i got an 83 xr500 engine which is an RFVC motor. it has dual carbs and exhausts.the bike originally did not have the RFVC motor but it had dual exhaust ports. i was told the exhaust pipe will not seal right on an RFVC engine. the pipe fits right into the head and looks like it fits though. i am confused. if the pipe i have won't work, will a pipe from an RFVC equipped xr600 fit it. now how about the engine parts. will the RFVC xr600 head fit on a RFVC xr500. i know the cams will interchange, i am pretty sure they would interchange. thanks.