They were designed by the railway's Chief Mechanical Engineer, Charles Collett.
On 31 October 1961 she was moved to Llanelli and fitted with a double chimney and a 4 row superheater.
It is worth noting that although Cadbury Castle was of GWR design, she only served with BR, as she was built 2 years after the railways were nationalised.
Cadbury Castle formed part of a Hornby model railways train set, The Western Pullman.
In this set Cadbury Castle was featured with four Pullman carriages and part of Hornby's Track Pack system.