Sorry to hear about your dad.
Not my area to be giving advice on, but as a collector of other rifles that have wood stocks (m1 Grands ,civil war muskets, etc)... I would leave the condition as is and let the next owner decide if they want to use other chemicals on the wood. I definitely wouldn't try to remove the patina from the wood. It looks like ti was converted from Flintlock to percussion cap at somepoint in time
If you do not get the information that you are looking for... I'd bring it to the civil war show in franklin, tn http://www.mkshows.com/
It's the largest civil war show in the country and someone there should know about weapons from your rifles era.
a few results I found for Josh Golcher Kentucky long rifle muskets https://www.gunauction.com/buy/6134398
https://www.invaluable.com/auction-lot/josh-golcher-pa-flintlock-musket-or-fowler-23-c-80d7b8f896
https://worthingtongalleries.com/shop/memorabilia/american-civil-war-memorabilia/19th-century-half-stock-golcher-50-cal-kentucky-long-gun/
Very cool piece, it would be hard for me to let it get out of my family. I hope you find a good home for it.