I've some colour photos in A book of "Great Western Coaches" by Kevin Robertson. The K40 in there is in TPO colours and also has the offset corridor connection. But there are photos of K41 and 42 (no idea of the difference between the diagrams, presumably someone in the drawing office moved a door handle!). The 2 photos from Karhedron answer a lot of my questions. In other words, lining the coach is going to be a pain in the arse. It's interesting that nearly all the windows have safety bars in them, but most of the windows are open!
Chris
From the photo at Didcot you can see what you mean about the bulging sides on the coach. The Comet sides could be manipulated to such a shape, but you'd either have to etch new ends or be left with a horrible filler job. And...let's not forget, K40 was bow ended.
Thank you gentlemen, very helpful. I'll put a picture up of the finished coach, probably June time.
Mike