Several people wrote asking about the picture of the brazed tubes. I double-checked and the proper term is “bronze welding.” And yes, the welds shown really were made with a gas torch – by an incredibly talented craftsman. The full explanation is below, though the SCCA reportedly does not recognize a brazed (or likely, bronze) welded chassis as legal.:
The heat source for all high strength brazing must be gas as there is no high strength alloy that survives in the heat of an electric arc. Tig brazing rod only has about 30,000 psi. The classic filler rod is Sifbronze No 1 (about 62,000 psi) manufactured by Sif welding products in England and a bit of a bother to get in the USA. Here, the answer is Eutectic Castolin, a developer and supplier of high performance welding and brazing alloys. Their filler is Eutectic Castolin Xuper 18 XFC® (about 70,000 psi) a bit stronger but a bit less ductile. All the normal caveats apply, you must have clean well fitted joints and you must form an adequate bead. These fillers will not work if you just flow the rod into the joint as though you are soldering. You must have a bead that looks the same as a weld bead only larger, hence the name “bronze welding”.