You should listen to me. No, seriously, listen to me.
Join Date: Oct 2008
Location: Santa Barbara
Motorcycle: Blue 2006 GSX-R1000
Re: OE 05'-06' muffler on a 03'
You'll have to search around here but I vaguely recall that there's some sort of issue with swingarm clearance when putting a K1-K3 slip-on onto a K5/K6. You're going in the opposite direction so there might be cowling clearance issues with it.
Check the parts fiche to see if they use the same EXCVA. You're probably OK if they don't but it would be one less thing to worry about.
Depending on the manufacturer, there might be db killers that you could add to your current muffler.