John James O'Hara from Tara and Mickey McNamara from Mayo "are famous Irishmen no matter where they go." Now "we're returning back to dear old Erin's Isle"
This sounds to me as if O'Hara and McNamara were musical performers who went to the United States. There was a John O'Hara responsible for a 1941 music, "Pal Joey" (see Gilbert, LostChords, p. 353); with so little background from Tunney's song, I doubt we can tell if they are the same. It doesn't seem very likely. I can't find any candidates for McNamara. - RBW