oem r6 tails are pretty easy to get onto fzr600 subframes, and you can still use the back seat. The one EMC is talking about is made by Airtech. not a bad tail, but it's solo only. Don't know if having a backseat matters to you or not.

yzf600 gas tanks (and motors) are easy to put on those bikes too. I can point you to a buddy of mine with a crazy fzr600 that caould probably give you any info on swaps for that bike you could ever need. I believe he even did a swingarm/wheel swap from an r6 on his too.