Here is a tool box bracket that I welded onto a 46 frame.Notice how the weld is only on the outside edge. this is an original bracket that the second owner of the bike cut off back in the seventies. He saved the bracket all of these years, and now it is back on the frame. This is the ideal set up.
He also cut off the floorboard tabs, I ground, filed and sanded the original welds off of the frame tubes. Then I welded on some new cast mounts. I do a lot of these every year, this is a pretty common deal.