You should listen to me. No, seriously, listen to me.
Join Date: Oct 2008
Location: Santa Barbara
Motorcycle: Blue 2006 GSX-R1000
Is it a slip-on? Muffler only? The K1 has a bolt-on style with a flange on the mid-pipe that bolts onto the muffler. Your K5 muffler probably just slides onto the mid-pipe. So you'll also need a slip-on style mid-pipe. The next issue is the pipe diameter where it meets the muffler. As far as I know all Yoshimura mufflers (except some very special race mufflers) have a 57 mm (2Ľ") diameter there. But other manufacturers use other diameters so you're going to have to sort that out. Finally there's the mount. Yours is welded onto the shell. That isn't as adaptable as the more common clamp around the shell and makes it more likely that there will be issues with finding a suitable hanger.
I'd try to identify the manufacturer and get more information.