Is the only differance between an 09' front rotor and an 03' front rotor the diameter? Is the 03' 11.5" and the 09' 11.8". Other than that will they interchange?

 

Bolt pattern is the same with like 2000 + I believe, the 2003 bolt pattern is the same as the newer models anyway. But they can have issues swapping due to caliper location.
If your looking to put 11.5" rotors on your 09 be sure the pads are fully on the rotor. If they hang over you will have some issues and I suspect they would unless the caliper was moved down in some way.

 

Thanks for the input. I plan on trying to install an 08' up rotor (the one off of my 09' SB) onto an 03 hub that is connected to the 21" rim that I want to install. I haven't had a chance yet to tear into anything. I was thinking of maybe ordering a nicer rotor before I do the install from KCint.com.