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Jane, I've checked my files to see if I have anything on the Percivals in Counties Leitrim or Longford, but darn, I don't find a thing. I checked the online church records at Irishgenealogy.ie and found the St Thomas Church of ireland, Dublin, 1891 marriage record of Henry Percival, of 68 Lr Gloucester St, Dublin, and Longford, farmer, son of John Percival, to Selina, daughter of Henry Stephenson. If you haven't checked those records yet, it might be worth a look.
I hope you continue your search and find something soon. Sorry to not be able to help more.