If you look at the toe plate, it is simple but neatly decorated and attached with round head screws. When you look at the patchbox, you see very amateurish, rough engraving that no Sheets gunsmith would have done... and flat head screws. Even the inletting of the patchbox is rough, and the hinge is non-typical. The sideplate suffers from the same amateurish engraving that no Sheets, or any accomplished 19th century gunsmith, would have done. I think you have an original rifle that has been significantly "enhanced" in recent years by someone just starting out to engrave and inlet.
Shelby Gallien