John, I don't know if this will help, but the coincidence is interesting...first I've just started dabbing in genealogy so bear with me.
The coincidence is that I'm tracing an Ellen FLAHIVE who had married a Michael MCGRIN. Ellen and Michael immigranted from County Clare, Ireland in 1853 or 1854 and settled in Crawford County, Iowa. Their farm was NW of what is now Manilla, Iowa but they are buried in the "Old Catholic Cemetery" in Denison. The interesting thing is that when my husband and I visited that cemetery several years ago we took pictures of their grave. Next to their grave was buried a John FLAHIVE. I assumed he was Ellen's brother. The tombstone said that John died Dec. 10, 1875 at 62 years of age. I think that would make him a generation older than your grandfather, but he may have been related to your gggrandfather. John FLAHIVE was the only FLAHIVE in the cemetery but many of the graves have been moved to the new cemetery so there may be more FLAHIVES in Denison. Unfortunately we didn't get to the new cemetery.