Dick, There are two variations in Sam Henry, see also 'Dark eyed Molly', and the one called 'Farewell Ballymoney' was Andy's source. There was a time, before any of the Sam Henry stuff was readily available when Andy, and possibly Paul Brady, used the set of the articles and typescripts that had been sent to National Library of Ireland by SH in the 1940s - check out Mary and the Soldier, The Rambling Suiler and others.
As to the song itself, it is a variant of a song widespread in the north called, Going to Mass (or church) last Sunday. (See the list of alternate titles and references in the 1990 Sam Henry - which is available again from University of Georgia Press; print on demand - English booksellers have it at reasonable rates.
Sorry you missed my talk in Ballintoy - I had nothing to do with the publicity.