Jers06C6

Currently I am running 305's in the rear with a 1/4" spacer to push them out to the fender a bit more, but would like to run 325's. I have C6 Spyder wheels but I do not know the spacing as they were on the car when I purchased. I will be changing out my wheels to Cup wheels and I am trying to figure out what the spacing would be to run a 325 tire. Anyone running this set up? What is your spacing on your wheel and could you post pics so I can see what they look like. Thanks