My guess is that Brideswell is the BMD registration area. The parish you actually require is Drum Parish, Co. Roscommon, now part of the united RC parishes of Drum, Clonown and St. Peters Athlone. I think both families came from there, though there are Keoghs in all S. Roscommon parishes. From memory, Drum Parish History has 4-6 McManus families in 1850 in Nure or Ardnanure. and there is certainly at least 1 Keogh family in the Parish. This household head name is Hugh Keogh. When you get to Athlone, visit the Library and ask for " Drum and its Hinterland" from the local history section. Just in case the book is out on loan when you visit, you may be able to find it on Amazon, or an Irish booksellers site. It is listed on Amazon, but what is availability is , is another matter. Somebody mentioned McCooey.....probably McHugh, perhaps family of Hugh "Hughie" Keogh. M(a)C means son or descendant of.