Do you remember the rings made by Lehman circa 1960? I first saw them in Gun Digest. They were to fit internally adjustable scopes to target bases. I had a set on a 44 1/2 custom with a quarter rib that was essentially a long target scope block. The Lehman rings are split vertically, held together by four small socket head cap screws - maybe #6 x 1/2". If you machined locating pads into the sides of the rib, there would be almost nothing to see when the scope was off. Disadvantage is that you have to sight in every time the scope is reinstalled s the rings will be off the scope.
I will photograph and e-mail to you the scope mounts for my take down high wall by Classic Arms. They are tip off incorporated into a rib, somewhat like the above photo of Smithson's. There are plugs to fill the holes when the scope is off, so vey clean appearance.
