The incident took place 4 May 1921. The man they were trying to rescue was Frank Carty. (See Wikipedia.) The priest involved was Father McRory (not McGroray). I don't know what to make of "Mack Jay" and "Sandy Man."

There was a book written about the incident: Coyle, Stephen (2008). "High Noon on High Street: The Story of a Daring Ambush by the IRA in Glasgow in 1921". ISBN 9781873586440.

From http://www.theglasgowstory.com/image.php?inum=TGSA05246:

An 18th century Bailie confronts a poster with 20th century news, in this cartoon published in The Bailie in 1921.

The cartoon reflects the outrage felt by many Glaswegians at a violent attempt to free an IRA prisoner from police custody. Frank Carty, a senior Irish Republican Army officer wanted by the Irish police, was arrested in Glasgow. A police motor van was taking him from the Central Police Court to Duke Street Prison when thirty armed men attacked it in Cathedral Square. Inspector Robert Johnston was killed in the first volley of shots and Detective Sergeant George Stirton was wounded as he and another detective returned fire. The attempt to release the prisoner failed.

Thirty-four people were later arrested, thirteen of whom were sent for trial. The trial lasted eleven days and hinged on the question of identification of the accused. The jury accepted the plea of alibi for the defendants, and they were released. Carty was sent to Dublin.