British double shotguns from early 1800s on both muzzle loading and cartridge guns up until at least WWII have their ribs soft soldered on and with far less bonding area than on your barrels. I think your big concern will be whether the two barrels are soft soldered or brazed together. If they are soft soldered, that join has to be carefully protected from melting while refastening the rib.
cheers mooncoon
Yeah. As an addendum, there is a lot of stuff done in production with induction heaters, that is impractical to do on a one at a time basis when trying to fix a single problem.
Induction heaters can chuck a whole lot of heat in to a small area, and melt brazing or silver solder, without affecting the joints of previous work. Typically the area to be joined would be buttered with a mixture of solder or brazing metal and flux, the parts clamped in place, then cycled through the localized heat to finish the join. Prep work and near perfect cleanliness are key.
Drag a thumbnail through the solder used, to see if it is harder or softer than the thumbnail. That is a good start towards identifying what was used. If you can find an unobtrusive place where you can access the solder or braze between the barrels, a poke with a HB pencil point will soon sort out if the solder or braze is harder or softer, which will determine if it is relatively safe to apply torch heat to melt the solder as the rib is properly applied.
Sorry, no names for you. Have seen what a fussy pain in the arse job that ribs between barrels of double guns can be, as well as the fun and games that go with regulating the barrels to a similar point of impact. Might be as good a time as any to start looking for a good used barrel set and see if that will materialize.
Best of luck finding the right guy!
