I was born in Logan WV and lived about half my life on this or that for of the Big Sandy River in the heart of Hatfield/McCoy country. Here's a good article on the feud, and from what I've heard from both Hatfield and McCoy family members their stories average out in this piece to about as much truth as we'll ever know.
Movies have been made, books have been written and countless versions of the story have been told about the Hatfield and McCoy feud. This is the true and un-glamorized story told as accurately and honestly as history, family records and local knowledge al
knoji.com
I figured that story might help you decide on a knife. I suspect that both knife and pistol had to be worn concealed under one of those boxy suit-coats and baggy trousers most of the time, especially in town. Your gun needs a holster, and I'd guess something like this on a plain wide belt would be about right:
epsaddlery.com
Remember that Devil Anse was a wealthy man by mountain standards. I don't know if he'd "go for any tom-foolery" as far as decorating knife, holster and sheath (IIRC, the "black" SAA was Colt's least expensive model). Folks in those parts are pretty pragmatic about such tools and were more likely to buy a fine rifle or shotgun if they had some money to burn. Then again, I'd have to dig up some photos of him to know that with certainty. You might strike up a conversation with the members of the closest NCOWS.com, they're the association of Old West shooters that strives for historical accuracy, and I bet they can even dig up some photos of him. There's at least one of him and his clan standing on the Logan Courthouse steps, but I imagine there are more.
Interesting project, please keep us posted!