Valentia Lynches?

My uncle did quite a bit of research to find that some of our Irish ancestors are from Valentia. I have been trying to find records for my gg grandfather,John Lynch, born 26 May 1840. He came to the U.S. around 1860 and married Margaret Cuff, from County Wicklow, although I cannot find any marriage records in Pennsylvania, where they settled and where census records indicate a marriagearound 1872, so not in Ireland. I believe that John'sfather was William Lynch and his mother was Catherine. Church records that I have searched online do not match the parents and birthdate. A sisterHelen or Ellen Lynch was born around 1849.

With such a common name, can you help me how I may narrow it down or where I should search next?

Thank you!

Deborah