Many thanks for all the replies with some interesting new sources I had not discovered.
I don't have access to Martin Welch's book that Lapford34102 mentions, I wonder, is the picture dated at all and what livery is it in (whiskers, SYP), please?
With regard to the Class 120s I was after details of any units, car numbers etc., known through photographs or other recorded sightings etc., to have worked on the branch in the early days of dieselisation.
All info gratefully received.