74 Duster rotted out drivers side torsion bar crossmember
I ordered a frame cap. The gauge metal was super thick, twice that of the OE metal. I did graph it in with a mig welder. I had to weld up around the T bar anchor. What made it a bit easier was the floor was rotted so I could weld both sides of the frame and cap.
Now knowing better having been there done that, I would not go that route but instead purchase metal in the same gauge to graph in.
I used a dremel/die grinder to get the thin metal out. When the normal thickness appeared all the way around, I used the cap on top of it. Get all the rust out on both sides if possible and treat it. The cap was plenty thick enough to weld to the T-bars anchor.
This thread;
http://www.forabodiesonly.com/mopar/showthread.php?t=10508
This area of the thread;
http://www.forabodiesonly.com/mopar/showthread.php?t=10508&page=5