Lewis Hyde and David Bollier of On the Commons ask the musical question: Where did Bob Dylan steal/borrow/appropriate/get an inspiration from for his songs and melodies and arrangements?
If you know your Dylan and know your folk music, see if you can tell them a thing or two.
For someone with more pro bono research time: I suspect the question has come up often at http://mudcat.org, on Usenet’s rec.music.folk (or a Dylan subset), and http://www.folkradio.org's folkDJ-l mailing list…
An earlier search produced this collection of more than 20 melodies Dylan used:
http://nwfolk.com/songlists/dylan.html