Just to let you know that there is a Facebook page.---O Shaughnessy gathering -Gort County Galway. It should be of interest to you.
Rory O Shaughnessy who was involved with I.R.O..in the past is one of the organizers of The O Shaughnessy gathering in Gort and surrounding areas. They plan to meet in Gort in 2021.
Rory has also done research into the O Shaughnessy families. Sr.DeLourdes' a genealogist in Gort has written a book on the parish of Kiltartan called
Kiltartan, Many Leaves One Root. A history of the parish of Kiltartan.
I also attach an article on the history of the O Shaughnessy and Cromwellian war.
I have found nothing on Findmypast.ie for any of the names John, Mary, Luke, or Delia.
Anne McCarthy Murphy