Hi dhawker. Have you tried "LMS Locomotive Profiles No. 11 - The Coronation Pacifics" published by Wild Swan in 2008? It contains a full set of drawings for a Duchess at approx 2" gauge, including tenders, the Ivatt locos 46256/7, & the streamlined casings.
There is also a photographic supplement, published in 2009 with the same title, which contains further drawings and photos of every livery carried by the class.
I hope this is of help.