A couple more pictures for you. The work is all complete now, and the van is back with me in Cardiff. All that remains is to cover the bed cushions with something suitable. 
This first picture shows the bed base that goes in the roof. This is curved at the bottom, but flat at the top. That's because Caravelle roofs are curved, whereas proper Westfalia ones are flat. 

This picture shows the pop-top on and open. The canvas is non-original, but isn't like anything I've seen before - it's a heavy duty canvas type cloth, with a sort of metallic-rubberised finish. Not a great description, but the best I can do! In this picture, you can also see the slight colour difference I mentioned earlier on.

The roof colour was produced using the vehicle paint code, but as you can see it's come out slightly lighter than the rest of the body. I was aware that the body sides (but not the roof) had been repainted at some time in the past, and it seems something went wrong! They either used a different colour, or the mix wasn't quite right.... but there it is - the original roof was a shade lighter, and now the new roof is also that same shade. If anyone has any bright ideas how to remedy this, let me know!