We did 2"x2" in my '63. We cut open the front of the rear framerails and slid them in a bit for overlap before welding. We also welded a plate to the front crossmember to attach the tubing. It was amazing how much difference it made! I can put a jack under any corner and still open the doors! I don't like cutting up a solid car more than you need to but this is one of those mods that do nothing but improve a car.