Most of the early B&I containers were 20' the 40' blue containers did not appear until much later below is a link to an O'Dea photo of a single 121 with a B&I liner
http://catalogue.nli.ie/Record/vtls000307819
Not only are they the wrong colour the vents on the model are the vents that were retrofitted by IE towards in the latter years of the Mk2's 5408 still has the original vents .
Wow another bargain,
https://www.hattons.co.uk/399823/Bachmann_Branchline_MM0184_PO_Irish_Class_181_184_in_IE_livery_Commissioned_by_Murphy_Models_of_Dublin_Pre_ow/StockDetail.aspx
Yes Mayner and reading your contribution I was reminded of the awful smell that once emanated from that factory which would hang about the place on a regular basis .
Great modelling