My experience is the opposite of
Griz44Mag's. I've had great success with a large aperture peep mounted in the normal rear sight position. It really sharpens the front sight for me (and my eyesight is manure).
However, it's fairly simple to fabricate a non-adjustable peep to mount on the tang if you're inclined to go that way. Here's one I made for one of my Hatfields (yeah, I know, I need to replace that round head bolt
).
I drilled and tapped the breech plug to mount it, but it could be put at the forward end of the tang, or even secured with the tang screw. A 12" x 1/2" brass strip from Ace Hardware gives you a half dozen sights with different aperture sizes and elevations.
https://www.acehardware.com/departments/hardware/metal-sheets-and-rods/sheet-metal/5024690