In the baptismal record in Avoch parish for March 1734, there are several men named Jack, and I found the following "alias" names, with all of them living in or near Seatown. Seatown doesn't show up on any more modern maps, but was then one of several villages, obviously on Avoch Bay.
Donald, James and a second James, all with "alias Gourlie or Gurlie"
Donald Jack alias Goodfeet
Donald Jack son to Wid. Jack
James Jack alias Coul
There were George and David without "alias", so I gather there must have been only one of each!
I can imagine what "Goodfeet" meant, but would anyone have a clue as to what "Gourlie/Gurlie" might have meant?
This same sort of nickname may be found in many families in Quebec, so I had an idea what it would be in Scotland as well.