Aww shucks, you guys are too nice with all the comments!
Here's a little more progress.
I was going to make a tang mounted sight but why reinvent the wheel? Not one of the older folding ladder sights but just a small peep sight. I've used the Skinner sight on my CZ 527 and like it a lot. It's pretty small and streamlined, the size is perfect for the Trapdoor except it needs a little riser.
Skinner sight and a chunk of 1/4" plate for riser. I used my cheap Chinese drill press with my cheap Chinese x-y vice with my cheap Chinese end mill bits to square it up.
Using my cheap Chinese belt sander and cheap Chinese moto-tool and Portuguese made files it turned out ok.
It actually fits flusher than it appears.
Not sure if I'm going to use silver solder or epoxy to get it to stay put.