Aberdare (Vale of Neath Line) in the 1960s

[RichardHC]

In the 1950’s and 1960’s I was living near Aberdare. In the early 1960’s I remember seeing, on a regular basis, a large freight train passing in the easterly direction near Trecynon Halt on the Vale of Neath line just to the west of Aberdare (High Level) station. This would have been in the early evening between 6pm and 7pm. I think the train was mostly composed of vans and was unusual (at least to me) in being hauled by a LM 2-8-0 8F locomotive. I think these LMS locomotives started being transferred to South Wales after a large number of GWR locomotives had been withdrawn.
If the train had come from Neath or Swansea if would have required banking from Glyn Neath to Rhigos and if it was heading to Pontypool Road would have crossed the Crumlin Viaduct with any weight restrictions there might have been there.
Can anyone tell me where this train had originated and where it was going to?