Thanks, Argo44. I note that even for an 1870-dated gun, the fences are very thin in profile.

The snap underlever is reminiscent of a design found on Beringer guns, I believe. Related to my query on another thread, are the various scroll-shaped underlever designs and the common scroll-shape of the trigger guard bow linked? It would seem the scroll-shaped trigger guard pre-dated the Beringer underlever, and Beringer (or someone else) fashioned a forward snap underlever that resembled the scroll shape of the trigger guard bow - or I could be wrong and it is the other way around - or simply unrelated. Trying to get to the origins of these designs is frustrating.