Another browse though the books reveals two three coach Bullied sets that might have been seen on the North Cornwall Line. (Possible for the Mawgan Porth to Exeter workings or even the ACE).
Bullied sets 768 - 769 were made up of,
Semi-open Brake Third - Seven compartment Composite - Semi-open Brake Third
These two sets had been transferred to the West Country from South Eastern Section in 1959. - An Illustrated History of Southern Coaches