Geo,
There are all kinds of ways to mount peep sights. I have mounted Redfield 75s, Marble Goss, and Lymans to the top of m/l barrels using a sight bar that screwed to the top of the barrel flat and extended back to the proper distance from the eye over the wrist. But, I don't know if you are looking for a period sight or just something useful that may not necessarily look "right". A good gunsmith can help you with this. Y'all may have to use your imagination in mounting it, but it
CAN be done.
NECG (New England Custom Gunsmiths) makes some of the nicest and best made
hunting peep sights I have seen. Also have the big moon bead for the front to go with it. Brownell's carries them. They are adjustable, too.
www.newenglandcustomgun.com SRH