9Three, fair point, Seyfried's rear sight was on the barrel forward of the action, but the point I'm making is that when viewed as a peep-sight in functionality, as the square notch should be, distance from the eye is not important at all because it is not in focus when aiming. Only the front post is in focus.

Having said all this, I prefer a tube-style aperture sight mounted on the breech-end of the rib. Although far from traditional, I have seen reference to peep-sights originally mounted on vintage doubles in a Brit collector magazine.

Failing this, a dove-tailed Shallow Vee further down the rib would certainly be a winner.

peter:
A bolstered re-regulated 12-bore ejector for $100Aussie sound like a bargain to me, no matter how ugly!

Then I can test that square notch sight out for myself.....