Yeah, I have to agree with Nerd about musicologists. I spent a fair amount of time in music schools (University of Washington School of Music and Cornish School of the Arts) and I've heard an amazing amount of drivel coming from musicologists about folk music and its early sources. Unless you find a musicologist who has made a specific, in-depth study of it, there are a lot of folk singers and folk music enthusiasts who are more knowledgeable (i.e., who can make guesses that are literally better educated, even if they did it themselves). With this material, it was the narrative that was important, and the tune was just the frame you held it in. This was why I learned about music theory, modes, and such from the music profs, but spent most of my time learning about ballads from Prof. David Fowler in the English Department.

You'd probably be better off with a professor of Early English Literature.

Don Firth