Do you know when your great grandfather was living? I looked in Griffiths Valuation for Co. Kildare and found nothing. I then looked at Irish Ancestry Surname Search http://scripts.ireland.com/ancestor/surnamehttp://scripts.ireland.com/ancestor/surname which is based on Griffiths Valuation of Ireland as well. This revealed several people with the surname Swanton but sad to say there were none in Kildare.
There was one each in Co. Fermanagh and Dublin City, two in Cork City and 76 in Co. Cork. It might be possible to search further with a date, the branch of the Christian religion followed by the family and any piece of information, however irrelevent it may seem to you, regarding those family stories. Where did he marry your great grandmother .. was that in Ireland?
I have a friend living in Leixlip. She is not really interested in genealogy but might know of someone in the area who might be able to help.