Hey we can use the zr1 wheels in an 18" wheel. Corvetteguys.com shows them at the correct backspacing. I think they fit Robin used a set of Z06 style ones this month in HotRod. Use the 18x9.5's and a 295\45\18 tire and that is about the same all away around as the factory 20's. Only problem is there is not too many tires in that size.
Hey milk I think we are screwed on the ZR1 wheels. Looking at the offsets that are offered for the ZR1's are +56 and +61 for the 18 and 19 combo. Just thought Id let you know since we both loved the Zr1 vette rims.