Thanks for the thoughts, Carl.
Yes, that's a nice way to get Polly Ann from Margaret, through Peggy Ann, but it does not account for the occurrence of "Maggadee/Maggie D" and "Mary Magdalene," which have actually been collected. To my knowledge, "Peggy" and "Peggy Ann" have never been collected.
I suspect that there were Isbell and Howard houses in the area at the time. I have talked with some Isbells and Howards but not about white houses.
I had not thought of "white's house." It is not immediately obvious to me how I could pursue that idea.
I think that singers and hearers of "white house" immediately think "White House" and that that makes the "white house/White House" stanza attractive enough to be preserved in tradition, but a literal interpretation, that they took John Henry to the White House, is fanciful. I doubt that the white house in the song was originally a reference to the White House. Unfortunately, there too many white houses around to allow a reference to one to have much value as evidence.
I take it that you are from the Dunnavant area. Do you live there now?