I bought some ralley rims 15x7's that say 15x7 JJ on the mounting area and on the side it says GM K 1 5 or GM K 1 3 What does this mean? Are these corvette rims? Also what size tires can i get on 15x8 on the back for a 70 chevelle b/c i have centerline 15x? or backspacing? 257/60 ends up getting cut in the wheel well. So i don't know what to put on a 15x8 stock ralleys. I am looking to buy 2 off ebay for the rear of the Vell.