Thanks for all this info Jhb. As a follow on question:
I am planning on running this b'n't 6 wheel brake van at the end of a train of b'n't MM cravens and b'n't IRM Park Royals pulled by a silver or b'n't CIE roundel diesel A class. Sometimes also pulled but a IR livery 121. Would this be close enough to prototypical?
And as my layout is a dead end branch line, once the loco does a run around to the other end of the carriages for the return journey should the 6 wheel brake be run around to the new back end of the train as well?
Many thanks