Does that read 1963 stock rear? If so it's a 4 lug unless it's been re-drilled to 5 lug. 4 lug will really limit your wheel selection. 235 tires are about the widest, no rub, option with no modifications to the wheel tubs.
My 63 SS came with 14” 5 lugs i think i used 245/70/14. Not particularly large, i know.
Had to hammer inner fender wheel well a little bit.
Used a brass mallot and a pressure treated 2x4.
But i was a kid
What did i know