I took the rifle down to Al Edge today for his evaluation and repair. He was quite impressed with the overall quality of the rifle and said that based on the stock hardware, the style and quality of engraving on the hardware and the type of stock finish, which he said was most certainly the original, that he estimated it's production date as sometime in the 1840's.
He took the breach plug out and found it and the threads to be in fine shape. The six grove rifling in the barrel was strong and when held up to a light, not a rust pit could be found. He also replaced the nipple, then gauged the barrel for rate of twist. It came to 1 turn in 25 inches (!), and he checked it once more to be sure it was right. I left it there with him to install a new front sight, widen the rear sight notch a bit and replace the elevating screw, and fix the broken inside prong on the right side wedge escutcheon. He has a range on his property, so I'm looking forward to trying it out when I pick it up.