[scottj]

BVM,
EM would have given you a conservative recommendation. If running the largest tire and wheel combo that the car will "tolerate" is your desire, I would suggest borrowing a Vette wheel, mock it up, and take measurements. Thats what I did. The first point of interference in the rear with regard to backspacing was the hub carrier. Even factory Corvette Grand Sport wheels rubbed the hub carrier where toe adjustment rod bolts to it. Remember the GS wheel maximized backspacing to run an 11" wheel with the stock width Vette body. I clearanced that area on the carrier with a hand grinder. In front the frame is the first point of interference.

I would be very concerned about narrowing the suspension any significant amount. I haven't run the vette suspension in my suspension analysis software but it would be interesting to see what narrowing it would do to instant centers, static and dynamic roll centers, camber gain, etc. Dick Gulstrand who has done alot of work with the vette susp recommends narrowing it only a very small amount to keep effects to those areas to a minimum.
Scott