I haven't heard Cyril's version. I just checked on Amazon, it's not available there: any idea where I could buy the album.

The version I posted above, I have never heard sung. I got the words from Co. Clare Libraries a few years back. They also gave me the lyrics of the CM version, pretty much as he sings it, including the wrong date.

The men were arrested in hiding at Williamstown [Big] House, Co. Clare (not Williamstown village in Co. Galway). Mike Egan, one of the murdered men, was employed there as a handy man and he hid the IRA men in one of the outhouses. Somebody informed the Tans, they approached the House from a boat on the Shannon, circumventing the IRA's lookout system. They took them down "by steamer on the lake" to the Lakeside Hotel in Ballina, not Killaloe. There they interrogated and tortured them. Just after midnight, 17 November 1920, they took them onto the Bridge across the Shannon and shot them. Each had at least 17 bullet wounds. The Tans said they were trying to escape.

Willamstown House was burned down the following year, tho part of it was salvaged and, last I heard, was being used as a place from which to hire pleasure boats on the Shannon. Like you I have visited the spot and seen the memorial on the Bridge.