In chatting with a new Walsh cousin in Sydney, Australia - we got on to the branch of Walsh's that seem to originate from Ogool and Finnaun north of Spiddal and west of Moycullen. I am not sure I'm blood related to them (yet) -- as my Sarah Walsh marries into this family, but it seems plausible that it's another case of Walsh's marrying Walsh's to keep it "all in the family".
To confuse matters there are two Uggool's. One in Killanin Pairsh and one in Moycullen Parish.
The David Walsh that Sarah marries, is from Uggool, and from his marriage record his Father is John Walsh. He is from the Killanin Uggool -- which borders Finnaun and Letterfir.
In the Moycullen Uggool - In the Griffith's valuation there is a Joseph and Thomas Walsh who are listed as tenants. In Tithe Applotment Books there is a James Walsh in Ogool -- could he be a brother of John? I also found a burial in Moycullen in 1799 for James Walsh of Ogool.
In the Killanin Uggol - There is no Tithe Applotment Book, but in the Griffith's Valuation there is a Mary Walsh (probably a widow, and possibly David's Grandmother?). In the 1901 Census there is a 91 year old John Walsh still living, which is likely David's father. David and Sarah are in Finnaun in 1901, and he dies before 1911, with Sarah still in Finnaun for the 1911 Census.
More research needed, but need to concentrate on the Walsh's of Finnaun, Letterfir and Uggool (Killanin) -- need to look for burials (probably in Spiddal Cemetery rather than Moycullen).