A couple images show no notch behind the hammer, and fresh/white wood where the current hammer scrapes the edge of the side facing above the lock plate. If you look closely at the lockplate cutout for the percussion side lug, the fit is not perfect, and in my opinion not as good as it should be for an original lock on this rifle.
I believe we have an always-percussion rifle that had its original lock damaged and replaced by this "percussed" older flintlock. Well-made rifles, as this one certainly is, usually had even-width side facings around the lock... unless elongated at the front and rear in regional styling. A hint of lock replacement can be seen in the unevenness of the side facing above the lock, i.e., the side facing gets thinner above the lock's top edge, suggesting a second lock, the repurposed flintlock, was slightly taller than the original percussion lock and the old mortise had to be opened a little along its top edge. If it were also a little longer, it wouldn't be noticed since the sidefacing had extra length at the rear, allowing ample room for a slightly longer replacement lock.
Shelby Gallien