It looks like a one of a kind gunsmith made with leanings to Stevens rifles,
I'm leaning that way as well. The brass on the bottom of the barrel looks like a muzzle loader rod holder used to be there. My bet is that it is a converted muzzle loader, by an unknown smith. It makes sense that it was cheaper to convert a muzzle loader than it was to have a barrel made. Not unlike sporterizing an old Arisaka or Mauser.
Don't give up on finding a maker yet. Even if it is a conversion it is a unique piece of history and I think it is worth investigating further. Thanks for sharing your pictures.