Order of installation: Torque boxes then Sub connectors, or vice versa

torque boxes are like triangular boxes which are welded by the start of the frame part of the leaf springs(where the springs are bolted) and they help with the handling of the torque coming from the rear end. If you have anything over a 340 with decent power you should have them, but they are only an option. (racers usually use at least this and sometimes more)