Paul,
If I'm thinking of the right locomotive, "Dot" was used on Beyer, Peacock's internal 18" gauge tramway. Horwich works of the Lancashire & Yorkshire Railway used similar locomotives with added saddle tanks and "Wren" of this type is preserved by the National Railway Museum.
Drawings - you might be in luck, The "Museum of Science & Industry in Manchester" holds a large archive of Beyer, Peacock drawings so I'd contact them first.
If you need to know more, email me as I have a large collection of BP stuff (mainly connected with Garratts) which I'm sure has some info but I'll need time to search through it.
G