If the forarm lug is tight, I would clean the raised piece, clean the mating surface, and buy some low temperature solder. Put flux on both surfaces making sure you don't go beyond area or else solder will run there. Using a dowel of the same diameter as the rib, tap the rib back into place, it should lock against the forarm lug. Make sure everything is flush and solder. Doing this with the low temperature solder should not affect the bluing.
Brownell's sells the solder.

David