I love the Planxty version (actually it's the very song that turned me on to folk music other than blues), wish I could hear the Nick Jones. As for Christy adding his own words, well that's the folk process isn't it? I've done the same. I sing it to myself using more or less the Planxty tune but they do it in E (I think) and I do it in G because that's where on the guitar neck I could pick an accompaniment. I get by with G, C, and D plus a few inter-chord positions. There are some verses which have a variation on the melody which is a little higher. On those I have to play a G barre chord instead of the regular one, and that's probably why I've never made it all the way through the whole song. I could probably transcribe my guitar part to tablature if anyone is interested.