The Irish came in droves to Merthyr Tydfil, so you will find a high percentage of Irish there and in Dowlais. You need to realise that when the iron was coming to an end, that coal was being discovered in the Rhondda Valleys just over the mountian - almost - from Merthyr. So many people then moved there.
You need to be absolutely certain of facts, before moving into the unknown, so make sure that your footings are correct with a certifcate or like, and then try to discover more. Make quite sure that you have the coorect certificate too as it is easy enough to get hold of the incorrect one.
Cardiff was then a small port which became larger because of the iron and the coal being sent down from the valleys. Some Irish families went there too. So you will need to search in these valleys and Cardiff and area. They will presumably be Roman Catholic so would move in groups - find out where the older Catholic churches are - one in Merthyr and you may be nearer your goal.
You could also try the Glamorgan Mailing List for help, or search their archives.
I could not help but wonder why you were searching for someone alive today ;-)) then I realised that Peter Dineen was the name of our taxi driver!!
Hope this helps, Harry
