Sorry to be so late!
I am from a long line of Alexander Levacks who go back to the 1700s in Caithness, North Scotland. Lack of census records end my line there.
I believe the name is connected to the Maclea(y)s. In the 1600s some Macleays assumed the name Livingstone. The Gaelic phonetic pronounciation is "Vachc-Lay". (Son of Lea.) In Caithness Levack is pronounced "Lay-Vac". I wonder if some Macleas didn't want to entirely give up their name when they left Argyleshire for the North East......for whatever reason. Certainly the name is closely linked with the Stewarts of Appin, the Macleays and the Livingstones.