I think the 12" will fit, and it helps that the offset of the rear wheels will set it about 1.4" out from stock. The ZR1 wheels which are 11" have the offset that leaves the outside in the same spot as stock (+1mm), so these would leave slightly more room than the ZR1s, which, from what I'm told, require no modification.
I don't really care for the wheel sticking out from the side of the vehicle, but 1.4" is reasonable, in my opinion. The fronts would be just under an inch outward, from stock.
Here's the wheel calculator link:
http://www.sytyarchives.com/howto/viewarticle.php?article_name=wheel_tech.php&dir=exterior