I have two versions of the Johnson Boys, one which is fairly close to the original, I think, but at the moment I can't remember for sure what album it is on ~~ The Hillbillies, maybe. The other one is a somewhat "updated" version with some reference to WWI, done by the Tenneva Ramblers in 1927 or a bit later. I have no time to do any research right now, but I will keep it in mind. Since you mention it, it seems quite possible that they were historical characters.