Wild Skies,
I've been care-taking Purdey gun #950X for almost twenty years now. I do have the factory letter on it showing it was turned out in 1875. It is an unmessed with gun, wearing its 30" Damascus barrels, and the concave game rib is perfectly flush with that small concave portion that it abuts on the frame top. Can't but barely feel the joint with a fingertip. If I knew how to post photos (and had some on hand of that feature, which I don't) I'd post them. This is not to say that mine is the proper way, but it is how mine were done from Purdey.