I am sure that you have thought about this...
 

but in case you have not. Lots of the C5 track guys are running 4 Z06rears. I believe that are 18x10.5 on all 4 corners. Locate 2 more rears and run 315's on all 4 corners and then you can rotate. Since yours is mostly a track car you do not need the tight steering and can place steering stops to keep them from rubbing in the front.

Check out ww.corvetteforum.com click forums, then general corvette, then auto cross and road racing section. I think there are a couple for sale in the "race parts for sale" sticky at the top of the page or down in the posts somewhere.

Thanks Payton, been dreaming about 315's up front for a long while. The cheap way out would be notching the stock subframe for tire clearance but I am seriously considering the after market subframe route. I can get away with any subframe offering a 10" wheel width and still get away with 10.5 rims with 315's due to not being afraid to roll and stretch fenders or be concerned with loc-to-loc tire rub. I guess in that respect a dedicated track car has a bit of an advantage.