Thank you Spitfire for your thoughts.
I forgot to mention that the coach is also lettered for the Western and Atlantic RR (in black strip below roof), they both run on 16.5mm track, code 100 surprisingly, and although I acquired them in the 1970s, I suspect they are much older. I was aware of W&ARR and The General and had wondered if the models had any link in with the 1956 Disney film..............
I'm sure in time someone will know.