Duffys from County Sligo, McGuffs from County Mayo

My great-grandfather, John Owen Duffy, was born in April 1844 in  (we believe) from the Ballymoat area of County Sligo. He his father and two brothers  immigrated to Bacup, England around 1860, One brother remained in Ireland and was a priest. We believe John Owen's father's name was Luke.

While in Bacup, England, John Owen Duffy, met and married Julia Mary McGuff.  She was in Bacup, with friends, and was from the Tuam, County Galway area.  (Her father's name was Patrick, from their marriage documents.)  They were members of St. Mary's, Bacup.

They had three children in Bacup, Thomas Henry, Patrick Joseph and Mary.  They immigrated to the USA around 1870  and lived in the Quincy, Massachusetts area.  They had additional children in the US.

We do not know the parish names but do have information that the city and county information is correct.  It is super hard to find them in Ireland if we don't know the name of the Catholic parish.  Any help would be wonderful!