275/45r18 on non duster anyone?

It would help if we knew what body you want to put big wheels/tires on. So far, i know its not a Duster. That don't tell me much.
Edit: if you are REALLY going after 550 wheel horsepower, my guess is you will need as big a drag radial as possible, and 15s work better than 18s. You might consider 17s on the front, for big brakes, and 15s on the rear. It's done all the time.
I wouldn't plan on an A-body being a handling car, with 700 hp under the hood.