Did you ever get replies to your query.There are 260 Fitzgibbons in the Irish telephone book not including Northern Ireland.
25 of these are in Limerick, 1 in Caherconlish. Addresses sufficient for mail delivery
O'Brien, 251 in Limerick, 9 in Murroe, Limerick. 1 Fleming in Murroe, Limerick.
The Tithe Applotments 1823-1837 are now on line for Ireland:
www.genealogy.nationalarchives.ieGriffith Valuation:
www.askaboutireland.ie or a more simple version with just Parish and townland
www.failteromhat.com1901/1911 Census:
www.census.nationalarchives.ieAnnette Code