That is an interesting problem! I gave it some thought and the best way in my opinion would be to heat them up in a controlled atmosphere oven. with a very thin ribbon of braze metal and flux in the joint. Held by a clamp of some sort. Yes, you would have to relay the ribs. When Parker(and others) did it, the barrels were in an unfinished state, so scale was not an issue. Try to do it with a torch would probably net you a crappy job. I might be willing to try a repair for myself if I could buy one of these guns cheap enough. Always wanted a steel shot special!