I'm trying to figure out how much is too much salt(s) to my water in another thread so I'm no expert here but I can tell you the profile you might want to match is:
Calcium: 115.0 ppm
Sulfate: 55.0 ppm
Magnesium: 4.0 ppm
Chloride: 19.0 ppm
Sodium: 12.0 ppm
Bicarbonate: 200.0 ppm
PH: 8.0
For Dublin... if it is a dry stout... and Bicarbonate HCO3 is the total alk... and with a ta of 200 I'd say it is an outstanding characteristic of dry stout's character
Here I'll run distilled for you in beersmith and see how to get you close... again, I'm not sure what is too much to add. If you add too much your beer could suffer just by the nature of the salt. It could produce off flavors and I'm just not sure of the threshold... I messed with it in beersmith for ya and put in 11 gallons of water to be treated.
To get to Dublin like water you would have to add:
4 g of Gypsom CaSO4, 4 g of table salt NaCl, 3 g of Epsom Salt MgSo4, 1 g Calcium Chloride CaCl, 8g of NaHCO3 Sodium bicarbonate / baking soda, and 1.7g of Chalk CaCO3.
That gets you less then 10 ppm away from a dublin target from distilled water. Btw for me 1 tsp of Gypsom weighs about 3g but I use a scale when making these additions. Again, I don't know and hopefully someone else who does know will comment on whether it is ok to add this many salts. Or perhaps there is a better way to get to Ireland from distilled
Edit: My water question was answered by TH and he has this awesome spreadsheet:
EZ Water Adjustment spreadsheet
Use it to get your RA in line... Also, if you look at the sticky in brew science Bobby_M has an awesome video(s) on how to use that spreadsheet and adjust your water...