Peter,
Not specifically in 5" gauge, but there is a WD D type at http://www.wdlr.org.uk/wdlr/drawings.htm which claims to be drawn at 1:24 scale. If it hasn't been scaled down to fit a web page, you could scale up all dimensions, though would probably need to sketch it all out yourself.
If someone had a CAD version they had already drawn, then you could ask them to scale it up for you.
Regards Tom