What is the highest and widest I can go in the front and back without rubbing or a liftkit?
27"? 28"?

 

There are no 28" ITP Tires made, but the 27" tires will fit. The width depends on what wheels you mount them on. IF you use stockers, I would go with 9" wide fronts. Otherwise they will probaly rub on hard/sharp turns. With ITP wheels I think it will have enough offset that you will not have to worrie about 12" wide tires rubbing.