Very many thanks, RichL.
In my teens, I devised an idea for an 009 layout, based on what the CDR would have looked like if it had ended up in the 1970s as part of CIE. I had designed a scaled-down "Dutch Van", and a similarly scaled-down 121; THIS thing above, and in particular the solitary example which went to South Africa and thus must have been "Cape" gauge, intrigued me as to what CIE might have ordered in the 1960s to replace most of the old railcars!
(Must dig out my old drawing out of sheer curiosity, though I have since become "broad-minded" (5ft3) rather than "narrow-minded (3ft)!!).....