Dave,

Years ago I had much the same problem when I was trying to sight-in a 3" FA 454 Casull. I contacted Ashley Outdoors (before they became XS sights), Ashley Emerson was always happy to help me with solving my sight problems (Ruger No 1 and T/C Hawken). He suggested I try a tall sight that they made for a levergun - I don't remember which one. It was exactly what I needed, it required a little bit of fine tuning, it is still working great.
The other thing I can think of is: Bowen. He may have a blank sight tall enough for what you need.
Hope this gives you some ideas.

Still working on that pic.

todd

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