The two original fire damaged old guns I have examined that had wood ribs, had extremely shallow dovetails, and folded brass sheet metal tenons. This would preserve the strength of the wooden rib, since less wood must be removed to inlet the tenon. By the way, one rib was hickory, and the other appears to be either ash, or oak, it is too burned to be sure. If the barrel is thick enough you could use stake in tenons as well.
Hungry Horse
