Hooh! Lost of activity on this thread. here's what I know on this:

Firstly, Cold Blow is not Planxty's last album, just their third. This is important because it predates Paul Brady being in the band. I believe it's sung by Christy Moore there. Christy got it from Mike Waterson, who heard it and thought it had Irish connections. It is, obviously, an American song.

It's very likely that PB (which in my community means Peanut Butter, but which I guess means Paul Brady here) learned it at least in part from Christy, to sing with Planxty, since Planxty was rather like a pick-up band with rotating members for a while, and included both Christy and Paul.

The Irish words are a translation made by Proinnsias O Maonaigh, Francie Mooney, the Father of Altan's fiddler/frontwoman Mairead. PB has indeed sung them. I don't know if they've been published.

Nerd