It follows a pretty typical form of plains rifles coming out of PA. The Slotterbek (slotterbeck, slotter)brithers come to mind as pretty prolific makers that built guns twin to that one. Usually the slotterbek guns are marked "slotter and bro" in a little inverted V on the top flat. Sometimes they will be marked with the distributor they were being made for ie AJ Plate. That gun really looks like a slotterbek which is why I had mentioned it when emailing. All the best
Zack