This vehicle was a one-off, and if there is a drawing it will now be at the National Railway Museum at York. (http://www.nrm.org.uk/home/home.asp
), as they are the repository for all things (UK) railways.
There is also a Glasgow & South Western Railway Association but their website seems to have ceased - see my pm for a possible contact.
The book you mention has been replaced by another one and tha quite good drawing now appears on page 131; there is also a small photo and that seems to show leather panel backed half shoulder height loose chairs. almost certainly with arms. They would be polished wood, very like walnut color. The other side is as the small drawing below (that is the kitchen area); reverse the main drawing and substitute the small bit on what is now the left of center portion. It appears to be either classless, or one (first) class.
I think that this diner would have been built for the very competitive Clyde coast traffic with both the North British Railway, and of course the Caledonian Railway. The train it would have been in is with the as drawn corridor composite coaches (& possibly some first class (your parlor) only as well). The engine for the Clyde Coast traffic would have been the massive Baltic tanks, which were very unusual as they had a planished steel boiler cladding (very like Russian Iron).
It would have been painted a deep maroon, very like your Tuscan red, and then lined out in black with gold edging to the panelling, and a grey roof.
The cross border traffic with England was in the hands of a joint company with the Midland Railway of england and the colors of it were the same as theirs; though the engines were a green color.