The only possibilities I could find to potentially identify this 6W brake van are 315A, a PW van/sleeping van, previously GSR 70 built 1888 as a former GS&WR passenger brake, 6-wheel, 30ft, one of eleven, b. 1882-99. Record seem to indicate that it was converted in 1955 to departmental use.
The other might be departmental sleeping van 368A, formerly GS&WR/GSR 14, built 1911, as a former GS&WR 6-wheel brake, 30ft, one of 36, b. 1885-1911. Recorded as converted to departmental use in 1960 which would precede the introduction of B'n'T in 1961
These seems to be the only vans left by 1973 so other than 69 for preservation, this van must have been scrapped in that interval after 1967.
Ref. Irish Railway Record Society 174 The Last Wooden-Bodied Carriages of CIÉ (Michael Baker)
EDITED FOR CLARITY after post below