I suggest you check the book Los irlandeses en Argentina by Eduardo Coghlan. Many times reading my mails I check this book and I found out some connections between the families you are looking for and the family with the same name that came to Buenos Aires. In many cases I suppose is difficult to link one family to other, but in other cases one can see both families repeating family names, like in the case of the Bracken with the name Martin Bracken, others giving some details like the place where the emigrant came from and this can work like the first step to locate where your ancestor was born. I hope this help Alberto