Thank you Roger. Your contributions help me to re-evaluate the evidence I have.
I don't have the marriage certificate for Peter Gribben and Ellen McNally but I got all the details from the parish records at the PRONI in Belfast.
I have found a possible William Gribben renting land in Carnacavill and another (or same William) renting land in Ballyginny. Both in Maghera and both close to Brynasford which was their parish church. Peter was botn in Carnacavill according to his son's baptism.
William was a carpenter according to Peter's marriage certificate and I believe he may have worked (for a time) at Tollymore Park near Bryansford where there was a sawmill. One daughter was born at Tollymore.
In 1876, in the County Down Land Deeds, a William rented 4 acres in Clough, Maghera. William's son John was born near Maghera and his grandson Patrick William was born in Clough. I feel the evidence suggests the William in the Griffiths and in the Land Deeds is probably 'my' William.
I agree that Patrick McNally in King's St, Newcastle is probably 'my' Patrick. I also have a Patrick (same?) renting land in Shore Road. Patrick was a shoe maker and I have records of him from Newcastle directories in 1870 and 1877.
Kind regards
Alison