"Any more is classified"
That would explain the cloak of mystery. On the tape, they show examples of fuel tanks made in large quantities for WWII aircraft, and the tanks are welded together, and I believe that mounting tabs, are also welded on. The spouts, though, are mounted though a surface drilled hole and brazed to the surounding material. I was just a little surprised they wouldn't talk about the brazing material. The modern fabricator might TIG weld that kind of part, or machine an interface. Doesn't mean that would work better than the lower temp braze.