McGowan Decendants

I am looking for information on the decendants of John McGowan and Margaret "Peggy" Gilroy of Tawnytallon.  From the parrish  (Kinlough) records I could find, John and Peggy had 7 children; John (1844), Ketty (1845), Mary (1846), Dennis (1847), Bridget (1851), and James and Patrick (1853).  Based on the dates, there may have been 3 more children born between 1848 - 1850 - Possibly my Great-Grandfather Cornelius.

James and Patrick did emmigrate to the United States.  James to New York, and Patrick to Massachusetts.  James did return in December 1923 for a visit to Tawnytallon; returned to the U.S. where he died in May of 1927. His death certificate indicated he was a widow - but I have not been able to track down his spouse.  In 1915 a record indicates James had a niece "Mary Monahan" of NYC.  I have not been able to track the niece down.

James did become a naturalized citizen, and the address he gave at the time of his intent to become a US citizen was my Great-Grandfather, Cornelius "Neal" McGowan (circa 1850).  I am trying to determine whether James and my GG were brothers, or some other kin.  A James McGowan was also a sponsor named on one of the baptismal records for Neal's children.  I have no way to confirm whether this was the same James McGowan from Tawnytallon. 

Anyone out there recognize the John McGowan family of Tawnytallon and whether they can confirm additional children for John and Peggy? Any information on other McGowan's from Tawntallon they were kin to John McGowan?  Attached is the Griffith's Valuation map of 1857 showing where the John McGowan Farm was located. Today the land still appears to be farm land -meaning maps show no roads through the plot.

Thank you very much!