The barrel flats on Tim's gun:




View of the breech:


I don't see anything on your gun that would change my opinion of its vintage. I would make sure your gunsmith is familiar with the design (warning-most gunsmiths are not) and have the work done that he advises.
If you are unsure, Kirk Merrington can work on it. So can J.J. at Champlain. Geoffroy Gournet can, too. Those are the three I would use.

Good Luck.

Best,
Ted