..............This is a copy of an old "Christie" aperture rear sight:
I added the piece of ruler for a scale.
View from the top.
View from the back.
All the parts.
Closer view of the Peep assembly. You can see that by loosening the aperture and re-tightening the aperture is how you control the windage.
.............I didn't post any dimensions or thread pitches, as your firearm will determine most of that. The elevation/windage arm could start out as a slice from a suitable piece of angle iron.
A round action would prove to be a bit more of a problem. However a round action could be accommodated by soldering/welding a pair of horizontal bars, maybe 1/8" x 1/8" on the inside flat of the base to span the radius.
...............Buckshot