[flatbed67]

Thank you Advanced Design, for the link. The shrinking disc seems to
work very nicely, and I'll get one some day. Seems like it's a fast way to do it
too.
In this very case, though, it would have been a bit harder to do with the disc,
since the sheet metal had stretched in a way that had made it buckle down. No
high spots to "grind" with the disc. You could also heat the sheet metal with a
welding torch, but I think that might require some expertise to get it right.
Another problem in this case was, that you couldn't work the sheet metal in any
place you wanted or needed, because of the hood's inner structure.