Thanks, I found the same problem with finding towns/bergs in Franklin Parish, there had been a few that had name changes in the last 140 some odd years.
Also figured that the names, specificially New River and Blackjack, since they referenced Post Office, might be the Plantation owned by these Gentlemen, not the local town. And that the locals came to the Plantation PO to get mail and such. Just a guess on my end.
Thanks for the direction on the Blackjack PO.