That's brilliant John, many thanks.
I have good memories of the late 80's post DART era and did indeed venture out to Greystones in late 1989 with the hope of travelling on a 121 with the last push pull set.
Seems it was taken out of traffic earlier that year and I came back to Bray on a leased NIR DMU !
Looking at the public timetable I hold, the 3 sets that started at Dundalk each morning ran to Bray, Bray and Dun Laoghaire respectively. It does look as if the likely return workings worked back to Connolly and didn't mix them up with Howth workings, ditto the evening trains that ended up at Dundalk. So likely not push pull sets as you say.
TB