The sideslapper hammers look like the work of Andrew Beeman of Canandaigua, Rochester and later Livonia, NY. The lock layout is reminiscent of the layout of a double sideslapper on a Wm Billinghurst O/U. Billinghurst spent his career in Rochester,NY. That completes a search of vol. 1 of The New York State Firearms Trade. I'll keep digging through my new books!
Ed