You could also try the IRRS at Heuston (which I think was suggested above). I was there as part of an industrial heritage conference a few years back and co-incidentally, they had chosen the staff register of the Dublin Wicklow & Wexford Railway to display to the attendees - my great great grandfather had been a stationmaster with said company.
Sure enough, on providing his name, his entry in the register was found and confirmed to be stationmaster, based on the fact that he was on an annual salary as opposed to a weekly wage. I don't know if they have staff registers for the MGWR or not, but it would be worth asking.