From the research I've done on wheel widths, the Cutlass can swallow a 9.5" - 10" rim in rear with no frame notch and depending on tire size used, a 275/40 - 285/40 tire with a rolled fender lip. It's still tight. If you run good rear control arms which control side to side movement better than wore out stock rubber bushings allows tighter clearances. If you do a frame notch and/or a mini-tub then you can go 11" rear rim width and somewhere between a 305 - 335 rear tire.
On the front, something along the lines of 9" with a 245 - 255 is about max. Remember that unlike the rear which has to clear only up and down and side to side, the front has to clear both while also having to contend with these in a turning arc.
I know Vette wheels have a LOT of backspacing so you'll want to run adapters instead of spacers. Spacers are only safe (even with longer wheel studs) to no more than 1/2" due to the increased loads on the studs. That won't be enough for the Vette wheels. You'll need the adapters which have the built in studs which are thicker and safer since the adapter acts like an extension of the hub. These bolts to the hub and then the wheel is bolted to the adapter. I'm not sure how thick you would need to go but I've seen adapters over 4" thick and also used on (8 lug) Dodge dually pickups. One positive aspect of needing adapters is you can vary the placement of the wheels in the fender (side to side placement by differant adapter thickness) for the best clearance.
Good billet adapters are expensive, costing in the $300 range depending on needed thickness. Do not scrimp on cheap adapters! We are talking about your wheels and them staying ON your car, not busting studs and possibly causing an accident.
Sometimes buying an incorrect sized wheel and adapting them with adapters is more expensive than buying the correct wheels with the right offset/backspacing and not needing the adapters is cheaper in the long run. If you want a certain wheel that only comes in select sizes then they have to be adapted.
The latter is the same situation I'm in.
In all cases, buy the wheels asclose to correct backspacing as you can and MEASURE MEASURE MEASURE before you order your adapters! They are generally custom made and what you order is what you get. You measure wrong and you get to order (and pay for...) another set.
There is also the matter of the adapters being hub-centric (where the wheels are centered and supported by the lip on the hub) or where as the wheel is centered and supportedmy thecone/shaft of the lugnuts only. Some say the hub-centric is best but I've seen some trailers carry some big-azzed loads just being suported by the lugnuts.
Dang, I didn't mean to write a book, just wanted to pass along some info. Info overload?...if so...sorry!
