My very own F3 to 600rr tail build
 

https://cimg7.ibsrv.net/gimg/cbrforu...d47d4808e.jpegNotched the rear end of subframe and bent it up, filled it in, mocked up the support and slide bracket for passenger seat...
https://cimg6.ibsrv.net/gimg/cbrforu...285a7949a.jpeg
https://cimg0.ibsrv.net/gimg/cbrforu...361202c5f.jpeg
https://cimg3.ibsrv.net/gimg/cbrforu...aa6e7dd5a.jpegMost fab work done for now, time for some tattle canning 😜
https://cimg5.ibsrv.net/gimg/cbrforu...ad6f01755.jpegPainted subframe as well...and the tank!
https://cimg5.ibsrv.net/gimg/cbrforu...34bfa713b.jpegTadah! Finished product... still waiting on tail light to arrive so I’ll post pics of the bracket I’m building for it once it gets here...
https://cimg3.ibsrv.net/gimg/cbrforu...536a460e9.jpegAdded some quick decals
https://cimg6.ibsrv.net/gimg/cbrforu...eb0385651.jpegOut of order but here’s how the undertail looks before the painting
As common as this swap is, most of the pictures users have uploaded are either extinct or there is not very many of them... so here are mines, enjoy!

parts used:
04 cbr600rr rear tail fairing
04 cbr600rr front seat
04 cbr600rr rear seat
04 cbr600rr tail light
generic LED license plate light from eBay
welder
scrap metal from my shop

overal money spent on parts: about $100.00
https://cimg3.ibsrv.net/gimg/cbrforu...e350d5005.jpegWhen I first brought her home
https://cimg9.ibsrv.net/gimg/cbrforu...0de919137.jpegTear down, decided to rattle can it satin black
https://cimg3.ibsrv.net/gimg/cbrforu...1449017ed.jpegStill gotta do tank, but you guys get the idea...
https://cimg5.ibsrv.net/gimg/cbrforu...5f9dc9677.jpegTail and front seat mock up
https://cimg7.ibsrv.net/gimg/cbrforu...ce6c02826.jpegSo this is where the fun starts... pieces of flat straps pre drilled and used self tap screws to lign them up and hold them in place to make sure front seat slides in.
Lots of tack welding parts in and just eyeballing as you go...

hmmm cant figure out how to arrange the pics in chronological order.....anyone ?

You should be able to edit the post. Each image will have show up as a line of gibberish. It'll use square brackets but look something like this:

(IMG)https://file loaction.jpg(/IMG)

Then you can just cut/paste those in whatever order you like

Nice job with the tail swap. It really modernizes the look if the bike