Just to keep the obesession going! 2 things to add or update - spoke with Karan Casey last evening who confirmed that she learned the version she sings from the singing of Christy Moore (though she does change the tempo to waltz time) and in checking a Decca records discography, it seems that the Burl IVes recording might actually have been released in 1958, which brings it closer to Will Holt, though I still think the publication of Yeat's book in 1961 is his source. Could be both, or neither!