Thanks so much for all the contributions about the song and related matters.
The "shot them in pairs, coming down the stairs" is strange, although Tracy had shot two British soldiers. Perhaps it's a way of conveying that he shot them on his way out of the shop, or it is a conscious or unconscious reference to the amazing adventure of the raid on Professor O'Carolan house in Drumcondra, when Treacey and Breen DID shoot them coming UP the stairs (and outside in the gardens too) (My Fight for Irish Freedom by Dan Breen).

As for the Talbot Street event, with known and wanted men meeting in place under constant observation, and without even a back exit, it does seem that some of the IRA in Dublin got used to living dangerously and took risks they should not have. The irony is that Breen and perhaps Treacey were sent to Dublin from their areas of operation for a rest! Does anyone know the actual address in Talbot Street? It deserves a plaque if it hasn't already got one.