Thank you good folks for your most helpful steer, which has enabled me to find the families of my great grandmothers three sisters.
As an addition I found an entry in the Belfast Newsletter, dated 6 July 1830, announcing the marriage of Henry McCurry of Ballymacash to Sarah Bruce of Drumbeg. Of even more interest was that two of the children of the sisters were given the name Bruce!
My 'win' this week has once again increased my interest in tracing more of my family tree!