About a decade ago I used to spot on drives down south from a footpath crossing about half way up the incline, you could park on a small farm access road off the B4096 and sit trackside on a small embankment.
There's a footpath off Pikes Pool Lane just before the railway bridge (Grid Ref at SO 98080 70633) that leads to some useful spots and another footpath at Burcot Bridge (Grid Ref SO 98630 71303); you can get to either side of the line there. The footpath to the east of that bridge towards Vigo is worth a look too.