Thanks Ard for confirmation that the song is about James Daly. I suspected so, a line in the song is "a young Connaught Ranger lay sentenced to death" and I knew that JD was a member of the Connaught Rangers. The execution date was 2 July 1920 (according to O'Farrell's Who's Who book), JD was aged 20.

The song is quite a long one, I have a recording of it, if nobody can find the lyrics more conveniently I will transcribe and post, probably tomorrow.