another source of information about Tomás Ó Flannagh>aile, author of "Gabhaim Molta Brighde" and also "Dóchas Linn Naomh Pádraig", a hymn to St Patrick:
http://homepage.eircom.net/~oflannery/bio/bioTOF18461916.htm

another spelling of Ionmhain in verse 1 is ionúin but I'd say ionmhain represents the pronunciation better, at least in Ulster and Connacht dialects.
Bríde is the modern spelling of Brighde