If you had a welder you could cut the inner brace out to get to the roof and then weld the brace back in.
If I had a welder, I could replace the roof skin.......
what do you need a welder for?
just cut out the flat part of the brace enough to get behind the dent. try to leave the rt angle part of the brace in the truck, just cut the flat part.
once you have the most of the dent pounded out, just add a few strips of sheetmetal and pop rivet the metal you cut out back on. use the metal strips to bridge the gap where you cut.
it doesn't need to be that strong. it wasn't very strong to begin with or it wouldn't have bent so easily.
