Look closely at the third picture from the bottom....the rail of the gaurd has had a finger forged on the end of the rail and that is folded over the bow. To me, that's interesting. This was a full stock at one time, but the barrel's coloration and overall even wear and rust tells me that the fore stock left a long, long time ago. As for the lock, I can't prove in a definit way that it is indiginous to the piece, but having a multitude of backaction locks that are original, I could easily compare plate width, length so forth and so on. One thing I notice about backaction locks is that mostly (not always) those old backaction jobs are slender when compared to the present day L&R locks.
It may also be plausible that the smith may have migrated northward to ply his trade in other areas, not just Cincy, but
perhaps a farther bit west, Indiana perhaps? Perhaps he was trained of learned his craft from the southern regions.
I lean more towards the lock always being there. I haven't taken it apart, but it would be easy to remove the lock, take a look and take some more pictures. I just find it interesting and am seriously thinking of building a sister rifle, complete with brass lock and all.