I just bought 1.5x3 .125 rectangular tubing to make a set for my 68 Dodge Dart. I appreciate you posting the diagram as I'm doing a similar design. I am curious though, was your car a Dart Sport aka Demon? Unless the 73 Dart coupe body style really shortened up the underside my 2 door 68 Dart coupe (not a post car) needed 50 inch long pieces not 40~ inches.
