"Almost identical?"
Jack,
Sorry; I don't read music, but I have heard Junior play it on many occasions, even have several recordings of him doing so. I have have also heard the song. It sounds the same to me, but we might be talking about different songs.
Junior made the tune without being aware of having heard the song; but when the similarities were pointed out to a member of his family (a musician herself), she accepted totally that it was the same in different times.
Jim Carroll