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The 1901 census shows Cornelius O'Sullivan, a widower and plasterer, living with four children on Main St.
In 1911, Cornelius and his unmarried son Michael were listed as plasterers. Two daughters, Hannah and Clare, were also in the household http://www.census.nationalarchives.ie/pages/1911/Cork/Dunmanway_North/Ma...
Suggest you contact the branch library in Dunmanway to see if they are aware of O'Sullivans in town who are or were plasteres. However, since Michael ws unmarried in 1911 and likely died by 1950, you may not find a connection.
Tel: 023 88 55411