Dowlais Ammonia Tanks

[0083]

From Service Timetable analysis regarding the above, I have the following timing details;
Hereford 1235SX 1215SO, Pontsticill 1541 1551 W Pant 1601 1608 W Dowlais Central 1610
returning Dowlais Central 1700 Pontsticill 1720 1730 W Hereford 2035 (W denoting water stop). I believe this was a Hereford turn both engine and men.

There is a classic photo of this train rattling into Talybont on 27th May 1959 double headed by two Panniers on the southbound leg. Unfortunately, the leading one has lost its smokebox numberplate both are 8750 Class but the caption states 8727 and 8780. I reckon the former (train engine) is a misprint and should read 8787 as this was based at Hereford at this time. Did the Pilot work throughout or was it attached at Talyllyn? If the latter, 8780 would be correct since this was Merthyr based.

Can anyone confirm the locomotive workings?