I am also going to recommend you go sign up and post this over on American Longrifles forum American Longrifles - Home - a site dedicated to the study and building of the American longrifle . There are some true longrifle geniuses over there, far moreso that any other muzzleloading forum I've ever found.
Well I can say that looking at your pictures the architecture is not from the 1700s, at earliest I would date it around 1840-1850s, and appears to originally have been percussion. Something of that nature is definitely easier to determine from a physical examination, and it most assuredly was made by a gun maker of some sort. Are there any markings anywhere, like on the top flat of the barrel or on the lockplate?
Mid to 3rd quarter flint lock plates tended to be long and 'banana' shaped, and often retained with 3 plate bolts, then they started to straighten out a bit around about the time of our Revolution, they did almost universally retain a pointed shape on the rear end of the plate. Germanic styles were usually slim and faceted while English styles were more rounded, French styles were kind of an in between look, and by this time 2 plate bolts were the most common. Between the end of our Revolution and throughout the golden years the lock constiuously were refined and they slowly started to shrink in size, and in the country the English style became the most prominent by the 1810s. This is when the Decadent age of long rifles started. The era of grossly shaped stocks and extremely gaudily ornamented rifles. It was in the era that the lock started to become more rounded on the end, oftentimes terminating with a small 'nipple' shape finial, Think the Durrs Egg and Late Ketland styles here. Then came the percussion era, when rifles started going to strictly utilitarian in looks. Little to no carving, engraving or inlay work, a rounded rear to the lock plate, single lock bolt, universal use of the painful looking crescent butt plate.