As a bluegrass musician, I am familiar with the song, which was a standard
for the group Lonzo and Oscar.  ("Many many years ago when I was
twenty-three, I was married to a widder who was pretty as could be...").  I
have never considered a connection to Mark Twain, but I sure will be
astonished if someone can uncover one!  (If you work your way through the
genealogy of the song, the singer really is his own grandpa...)