Have you seen the reference on Irish Genealogical Abstracts by Donald Schlegel pg 87 item 624 Boyd Maxwell (married) to Margaret Gray both of Omagh (Co Down) dated fri may 29 1778. I am working on the Rev James Maxwell ca1670-d1750 married UNKNOWN (possibly Catherine) Boyd - Presbyterian minister Omagh ordained in 1700... I wonder if there is a Gray family living in Omagh in 1778?
Not sure about this Boyd Maxwell but suspect he is son. Many of this family immigrated to SC and Australia.
Do you know of a living male Maxwell from your Davids line...if so we can DNA test him and tell if he is closely related to this line.