Willie O is an Irish broadside song based on the older Sweet William's Ghost; you'll find plenty on it in older threads here, with links to broadside examples.

I don't know where Cathal got his set, and I don't have a copy of the album; a source of regret, as it was the first that my old friend Tich made with Boys of the Lough. Cathal's text probably wasn't very different from the other ones known, but perhaps someone who does have a copy of the LP would be kind enough to quote whatever the sleevenotes have to say on the subject.