Curt, I have been occasionally talking with other gun nuts about early barrel profiles, and we concluded there are a number of barrels with flared breeches, an upswept breech, and a bent down tang. This we term a 'humped' breech. This hump gives a very different stock architecture than the 'norm' PA rifle we are accustomed to.
I would say that this is seen more often in European guns than in America, but there are isolated American guns where this humped style breech shows up. Most likely these guns were made with imported barrels.
A banana lock would be perfect to use with the humped breech and downswept wrist.
Going out on a limb, A straighter breech section would be begging for a straighter lockplate. Changes in style and market demands would make the humped breech barrel obsolete, and the banana lock went with it.
I love these old guns and the thoughts they provoke.
Thanks, Tom