I can make out Ballybrack dolmen pretty clearly, its about 400 metres to the left of the mark on google earth. The co-ords from GE is 53°.14'42.16" N 6°07'20.80" W.
So the map's easting is out. Ballybrack is an easy one to check up on as are many other local sites. Gives me something to do when I don't feel like going on a big trip.