I have a method using the tithe Applotment Book records, which are sadly split for genealogical work. I have made an alphabetical index of last name entries for the 6 counties based on the parish listing by parish made by the Irish Genealogy Hub website which sometimes throws up both names of a later marriage existing in the same parish the odds of finding the two names in the same townland are even more striking . but could be spelt McGra
McGrath, Ed.-Townland: Kernan Year: 1834- Tullylish-Down
McGrath, Ed.-Townland: Miltown Year: 1834- Clonallan-Down
McGrath, Edward-Townland: Ballynaris Year: 1834- Dromore-Down
McGrath, Edwd.-- Townland: Drumkee Year: 1825- Killyman-Tyrone
McGrath, Edwd.-T: Dromore Y: 1834- Dromore-Tyrone
McGrath, Edwd.-Townland: Ballymagaghran Year: 1832-Belleek-Fermanagh
McGrath, Edwd.-Townland: Kernan Year: 1834- Tullylish-Down
McGrath, Eliz.-Townland: Portaferry Gardens Year: 1827-Ballyphilip- Down
mcgurk 160 and mcguirk17 entries had no match of parish in 6 counties with 177 entries in total
I didn’t check for McGra spelling
so you could try the same method forthe 26 counties covered by the National Archives Dublin
using
eg
http://titheapplotmentbooks.nationalarchives.ie/search/tab/results.jsp?surname=mcGuirk&firstname=&county=&parish=&townland=&search=SearchMcGuirk entries 28
McGurk entries75
McGrath, 1429 entries
You would need to copy the entries for each ten entries per page for each name onto a spreadsheet and eventually sort by county sort by county, finally only checking any further by both names in a county, then refining that to by parish and hopefully by townland and it mat still not be the true answer I think it has worked for about 20 missing locations in Ireland but even the record isn’t complete in itself, if you have two scarce names its much easier. I cant spare the time to do it for you. it’s a last resort for you. nevertheless i leave it with you.