I use 2x3 .083 and section it up into the floor. The rear half of the connector will slide into the front of the rear frame rail (on a stock rear frame car), be sectioned up into the floor in the passenger foot area, go back under the floor 100% under the front seats and butt against the rear of the torsion bar x member just outside the torsion bar sockets. This makes maximum use of the frame tie to stiffen and tie the car together. The main hoop diagonal can be attached right to the top of the connector. This diagonal is required on a full cage anyway and a good idea on even a simple bar.