I’ll agree it’s a nice old gun in nice mostly untouched condition, but remember that active rusting is not patina, it’s just rust. Same with years of dust stuck to the stock, it’s just dirt.
If it were my gun, I’d oil the dickens out of the iron and rub it down well with brass wool of a green kitchen scrubber, or some such thing to try to remove the active rusting. Just be careful not to rub through on the edges of the barrel flats.
It wouldn’t hurt to run an oily patch or brass brush up and down the bore a bunch of times either!
Don’t polish or buff the brass, just a damp cloth to take off the dirt.
For the wood, I’d take a damp cloth and run it over the wood. Just use cold water, no soap, and don’t scrub it. Buff the wood dry with a clean cloth then give it a light coat of clear drying cabinet makers wax.
It’s not surprising that the barrel has been reused. At that time period (1850-60s) lot’s of old gun parts were recycled into inexpensive guns for all sorts of uses, and I expect that’s the case with yours.
As such, it represents the beginning of the end of the muzzle loading era, with all sorts of new fangled breech loaders being invented during the civil war!
Thanks for posting the pictures!
John