That is a fine collection indeed. They are born of target shooting rules which didn't allow alteration of the rifle.
There is another for the Long Lee-Enfield which a friend offered me once for something else, in the days when they weren't as collectible as they are today. But I didn't have the heart to modify it. I believe it was a BSA sight, with an aperture and vernier adjustment, but it attached on top of the barrel, to the original open sight bed, and was held down by spring tension. I doubt if it was very satisfactory, as the aperture was slightly in front of the receiver ring.