Richie,
If you haven't already got a copy, among the extracts Jim sent me was Barre Toelken's 1967 study 'An Oral Canon for the Child Ballads: Construction and Application' which looks at the 135 Child Ballads found in reliable oral tradition. He uses principally, Coffin, Bronson and Keith as his sources to decide which ballads merit being accepted as folklore. If Jim hasn't got his copy to hand I can easily scan mine and send it. I think you would find it very useful.