I have seen several English DR's with the folding aperture at the spindle. All appeared original as I recall. All also had express sights which would render the folding aperure nearly useless.

I like the idea as put into service by McNaughton in Capt Curl's photo. But I would prefer the same set up with a 1/4 rib and another dovetail for an express sight for use before the peep became mandatory.

JPK