It's almost always the last bend that gets messed up! Murphy's law! It's especially tough when braking something up that is 10' or really big/heavy, and you need to rely on another person to brake up your material with.
I quickly learned to mark out my brake lines with different color fine tip Sharpe's and use a numbering sequence! Even with that you need to watch the other person like a hawk since most of the items I would ask for help with happened to be stainless, copper, or (special order) 10 gauge cold rolled. It was always for some rush job too!
I was asking about the thickness of the main flange since it looks like 1/2". The 3/8" thick material I've used in the past for flanges seemed like fairly thick stuff, but that 1/2" is much better for your application. The ones I used for VW applications were water jet cut and it always amazed me how "clean" they were (freshly cut)! I never even had to file them to get fasteners or tubing to fit inside.