Sometimes a bit of research with a purchased slide provides dividends. Here we see 20142 and 20030 at Treherbert with the 'RPPR' 'Deltic Dragon' Railtour. Ok they are not a Deltic but there was one earlier on the railtour.
More details can be found at sixbellsjunction:-
http://www.sixbellsjunction.co.uk/70s/780129rp.html
Slide taken 29/1/78
Photographer unknown.