Little is known about the exact panel layout, but I found one telling picture at least. The colored sections represent my interpretation of the possible course of the panel lines, based on the assumption that these were following the main frame. I need to point out that these are probably of a A-version and I dont know details about the differences at the time.
Here is one interesting "What If" scheme. I would surely try to find a way to combine this scheme with bare wood effects. This picture is one of a C-version of course, but a B-Version might have looked like that during design. I know, its a bit artistic but I like it that way. :-) Click to enlarge and save copy as...
In the following a few close ups of the Walther engine. Click to enlarge