front should be somewhere around a 275/35/18 and rear should be around 295-305/35/18, the stocks on the Zo6 are 275front/295rear if i remember correctly...so yea tires are more expensive but thats a trade-off for nicer looks...im going 19's and getting 285's or 295's on the rear depending on money but im looking at $300+ for EACH rear tire and they're only STREET tires

lol

but anyways back to you, the offsets should be fine if they're OEM off that ZO6 they should bolt right on. I doubt you will have a clearance problem but watch the rear if you go with a big tire(305/35/18 or bigger) if you're lowered it might "rub" on the "inside" of the wheel with the fender well and/or that crappy bump stop thing. Hope it turns out lookin badass man take it eazy