I apologize, A-body content!
I used 1.5"x3"x.120" tubing on my Duster. The E-bodies are a little more exciting because the connectors run at a slight angle from the rear rails to the front so they don't land on the torsion bar sockets, and the rear rails are slightly splayed. The rear rails are also slightly narrower (width of the rail itself), and don't hang down as much at the intersection of the floor. I used the 1.5" tubing because it basically laid flat on the floor with the rail against the inside of the tubing in the back.
Not sure if your class will allow the amount of overlap I used of the rails. I also plated the torsion bar sockets to match the landing plates of the subframe connectors, and keep the socket from breaking the welds at the crossmember (an issue with some A-bodies). Either way, fabricating your own connectors is pretty simple. I like how the ART connectors step at the rear rails, but that front overlap is as ugly as sin. Bigs has the right idea, I think you could make great use of some 1.5" x3" tubing. It would need more of a step at the back than Big's used, more like the ART connectors, but you should still be able to get them to land flat on the front crossmember since the ART subframes look to be 2x2. Basically it would look like the ART subframe connectors, but flat with the front crossmember and with a little less step hanging down in the back.
