The Cambrain Line was always classified blue, hense nearly all the the Manors being transfered here towards the end of BR, and the use of them on the Cambrain Express west of Shewsbury. The main reason for the restriction was originally the Barmouth Bridge, although subsquent maintaince ment that the whole line became relatively fraglie quite quickly.
Today the situation is even worse, with locomotives being banned from passing over Barmouth Bridge since the mid 1990s. Hense there has been no steam tours in the area since around about 1994. However, resent work by railtrack and tests with class 37s have ment that this restriction *may* be lifted in the near future.
We can but hope anyway....
Either way with its double red classification, Kings would have certainly never have been permitted here.
Castles and Halls were both classification red, so again were banned.
Motive Power in the area was mainly Manors, Standard 4mt 4-6-0s (come on Robin

), and Ivatt 2mt 2-6-0s . Also Dukedogs were very common, and a number of early GWR outside framers ended there days here.
Bruce