Thank you so much for this information, Patricia! This Alexander definitely does look the right age, religion and birth location. However, the name of Alexander's father and all of his siblings do not match any of his children or grandchildren.
My Alexander's children were Ann 1750, George 1753, Alexander 1755, Bridgit 1759 Hugh 1760. His wife's name unknown.
Continuing on... Alexander 1755 married Mary; their children were Charles 1773, James 1774, Henry 1775, Catherine 1780 and Alexander 1790.
Based on these 3 generations, it looks like this Alexander McMurtrie family line did not follow traditional Irish naming patters opening up the good possibility that Gavin could be his father.
One other clue to verify accuracy is... If Alexander (above) was the right one, He would have come to America when he was 7, so he had to come with his parents. Do you have any evident of Gavin and his children living in Ireland past 1723?
Also FYI, I have a pretty knowledgeable ancestry friend who suspects that Alexander could be possibly one of the Scottish Protestant settlers who had been sent in to Ireland to colonize the area after the Cromwell incursion. Do you know anything about that?
Thank you for your time and effort, Patricia.