Hi Adrian
Many thanks for the links.
I thought only 3 of the 6 K38s had OM lettering but may well have mis-remembered from reading my Russel books. From all of the research I have done so far, the OMs were included when needed so it stands to logic (or at least my logic) that if a liner with 1st class passengers arrived to be whisked away in their Super Saloons, it is not inconceivable the fast-mail would have been attached too. I guess it is one of those things we will never actually know now.
Re the Comet instructions, I believe they relate to post-1934 when 2 of the Supers were converted to have their own kitchens, Princess Royal and Princess Elizabeth if I remember correctly. I think H15 is a good bet although I do remember seeing a 1st/Kitchen/Brake which I believe was H11 (or was this actuall H15, my memory fails me).
Thanks for the link Industrial... I lknew I had seen a list like that somwhere. Very useful!