Beechpark or Beech Park, Templeogue

If you live nearby, go down the street and see if you can see a security hut by the gate of Cosgrave’s place. He gets this as part of his deal as a retired taoiseach, moreover one who was a strong law & order man in the lawless 1970s.

As to the house being bought or inherited, I don’t know.
His father, W.T. Cosgrave, lived in the area but possibly in another house.
But local people would be likely to know this too.

Don’t neglect to make an introduction that would bespoke your bona fides when making your enquiries.
There are still a few around who’d happily kill Cosgrave and you’d avoid unwanted “enquiries” about yourself this way.