If you keep the original outside tire diameter of close to 26.2" and maintain the original section width, nothing will rub. You can put 26" wheels, no tires on.
Go to
www.tirerack.com and use their tire size tables and different tire brand sizes to compare with the specs on the tire listed on your driver's door sticker. Don't forget, if you get crazy with tire sizing you throw the speedo and transmission settings off.
(BTW, the car will look and ride like hell.) Look at 18" Deville/CTS 10-spokes, max.
www.wheelcollision.com, click on the little pic to get a better view of each wheel.