Ahh... I see you made the trip from Antiqueguns. Those here will offer their comments and knowledge.
My impression is that you have the real deal. A very late period gun and quite possibly "upgraded" after the gun was out-shopped. I say this because I suspect that some of the inlays aren't original to the piece, though Leman would build semi-custom pieces.
In any case a nice in-period example of a long rifle.