If you have access to Irish heraldy material, especiall for the late 18th to early 19th century, please look for McCandless (may be spelled M’Candless, Mac Candless, McCanless, etc., etc.). As I’ve added to the Heraldry page, a McCandless coat of arms has been discovered on a grave marker, but it is missing colour information, being just carved line-art.
Regarding the grave in St Columb’s Cathedral of Thomas McCandless, the coat of arms is actually that of the Worshipful Company of Curriers, one of the London Livery Companies. Their motto in Latin translates as Our Hope is in God. This Thomas McCandless is also descended from the same branch which Sarah Adeline McCandless writes about. There is no connection with any of the Galway families. Unfortunately the coat of arms has no McCandless connection other then Thomas and as a prominent tanner and currier in Londonderry