I made paper patterns of the original brackets. Laid them out and carefully cut to shape. Before the 90 degree flanges were bent (hammer/vise) I just jimmied up some really crude temporary die offsets using flat steel scraps and some machining hold-downs (think steel bars/bricks). With everything clamped down to a table and hammered on to help enforce/define the off-set. Finally checking the fit on the truck I banged on them a little more to fine-tune. I think there's a rough diagram somewhere back in the thread I put up for somebody.
I don't know much about sheet metal work but I'm sure it would be a lot easier with even a small, cheap hand brake ($200 Grizzly, etc.) and a few additional tools. I want to build another steel "welding" table down the road and may try to incorporate a "home-made" simple brake into one side of the table. And maybe a Lancaster shrinker/stretcher set to also mount on the same table.
Hope that helps.