I've been checking for traces in Dinnydoon, Derrydoon, and Derry "from" Rossory without much luck. The trouble is that Thomas Maguire doesn't show up until that entry in November 1820 in Mullaghdun, Parish of Cleenish. Records anywhere are pretty sparse before 1820, and the family left for Canada in 1847, before Griffiths'. Seems to me the Tithe Applotment places him in Cleggan.
I still think you've put me farther ahead than I was.
Many thanks.
Carl