The angle iron is bolted to the pinch weld with 5/16 stainless bolts. Large washers on the pinch weld side to prevent pulling through. Before I drilled and welded I attempted welding them, but I dont have faith in my welds or the fact that I realized I was "welding" to sheet metal. So the holes were drilled through the pinch weld and the angle iron and the bolts went in.
I first placed the rectangular tubing on the angle iron then test fit it up against the rocker panels, holding it up there with a jack. Looked for anyplace that might not fit. (Brackets, bolts, etc) any "conflicts" I saw got a clearing cut in the tubing. Then the tubing was placed up against the rocker panel again. The angle iron was placed against it and everything was held up with a jack. I used a couple c clamps to keep the parts together as I "attached" the angle iron (the aforementioned welding). Following that the tubing was removed leaving the angle iron right where it needed to be. That's when i decided to drill and install the bolts. I welded end caps on the tubing, also filled any place that got notched. Then painted the tubing and the angle iron (except where they would be welded together) placed the tubing as tightly into the angle iron as I could then welded the edge of the angle iron to the edge of the tubing. Then painted everything again.