One of the IRRS journals had a feature on the Waterford-Rosslare line with pics of BD containers in open wagons.. I have also seen pics of some BD wagons with a label saying they were carrying car parts for BMC, likely for assembly of knock down kits.. I have yet to find pics of BD containers on flat wagons, only later ISO type 20fts on 20ft skeletal flats.. Maybe it was felt they couldn't be sufficiently secured on a flat wagon(no twistlocks/Corner castings)..
Will try find that article when I have a chance..
CIE did have later aluminium non-ISO containers, again I have seen pics but don't have them handy right now.. Not sure if they had BD/timber bodied ones, the GNR(I) certainly did as modelled by @leslie10646