If you are certain about birthplace being Bangor it may refer to Bangor Parish rather than Bangor, the town. If you go to the Ros Davies Co. Down Genealogical web site you can get a map of the parish which includes Donagahadee and Inishargie where McFerrans lived as well as Crawfordsburn. It might be worth combing through the "Sorted by name" web site. Your local LDS (Mormon) library may be able to help. Also check the McFerrans in the Lennon Wylie web site for Bangor town and surrounding places in the parish. If all else fails PRONI has a list of reputable professional genealogists who would likely find the family for you.