The name Lusk is found in Banbridge. A John Lusk is listed at Ballykelly in 1886. He was a farmer. It is a toponymic name from the village of Lusk in Co. Dublin but now mainly found in N.E. Ulster. The appropriate volume of gravestone inscriptions for Banbridge from the Ulster Historical Foundation in Belfast (web site) might take this family back further. Records in the 1730's are pretty scarce and gravestone inscriptions the most likely place to find ancestors from that period.