I say the best for looks and function will be going with some 19s in the front and 20s out back. YOu cvant go wrong here because you can still put a bit thicker tire in the back fro that big block torque.
Bill Howell has this same set up on his GTO but 12" wide in the back I think.
check it out.
https://lateral-g.net/members/howell/