From the details on his obit, as mentioned by Heywood, this looks a good possibility for his birth as it mentions that he was 89 when he died:
PATRICK FLANNIG(AN?) REILLY
1928
644/11 115
Anderston
It mentions when he was second youngest of 10 children.
It also states that his father died when he was 11.
For your father to be his first (?) cousin, a daughter of Donald mcdowall and Mary mcdowall nee Reilly married a Reilly?
Do you have the names of all the children of Donald and Mary?
Monica