Ok, seeing as I was the first one to do this swap....
If you want to fit the 325mm rotor (12.8") you use ALL the same parts except you source C5 rotors instead of the 12" rotors.
You need to use this bracket as well to space the caliper out correctly..
http://www.lgmotorsports.com/catalog...oducts_id=1556
Here's a detailed installation on a F-Body.
http://www.c-computers.com/C5-install/
On a side note, I'm going to see about a 14" brake upgrade using a C6 Z06 rotor and a CTS-V Brembo caliper. As well as using the 13" with the C5 bracket and pads instead of the F-Body ones.