I have enough vices, that I've stayed away from black powder muzzle loaders, so I would defer to Grizz and Andy here on this one. I trust your gunsmith had the knowledge to check to see if the gun was loaded? It wouldn't be the first time, if it was, and black powder can still go off 200+ years later.
I do have extensive experience in the preservation of old guns. I see a family heirloom that I'm sure you would like to pass down to the next generations. That stock needs a good cleaning and conditioning. Family value is priceless, no idea what collector value is. The point is, you want to preserve it, but keep it original as possible.
Rule of thumb for the brass hardware is clean, but don't polish. Leave the patina, brass only gets polished with a full restoration.
The stock can be cleaned and conditioned with boiled linseed oil from your local hardware store, and a piece of burlap. Soak burlap, wring it out, scrub the wood, and use paper towels to wipe it clean. Some old finish, smoke from hanging over the fireplace, oil, dirt, and grime is what the paper towel will be covered with. The linseed oil will condition and preserve the wood, add a sheen to it, and still look original.
Word of caution, anything like the burlap and paper towels with the linseed oil on it should be left outside to dry before you put them in the trash. With the drying process, the heat generated in a confined space by the oil, can cause spontaneous combustion.