I currently have 255/30R22 Lexani's on my 04 SS and all that was needed was about 1-1.5" lift on the front only. Other than that nothing is actually needed unless u want to.
Also you will need HUB CENTRIC RINGS to fit the rims flush to the hubs. Suggest going to a custom rim shop to get these (discount tire, ntb, ect... Wouldn't help me cause I wasn't going to let them do the work)