Thanks Paul, Gary, Joerg and Alexis, I'm taking the photos carefully to hide my varnish imperfections but it is definitely a very cool scheme. Whether it actually ever looked like this we'll never know.....
In regards to your research into the carb linkage, I?ve sent a picture to your Messenger account which hopefully may show you what you were looking for as far as linkage to the carburetor (saving the faff of uploading saved images etc.)
Thanks Gary, as I said I actually have that book and missed that picture. Although it doesn't really help because I found the original workshop manual for the BMW IIIa (
https://bmw-grouparchiv.de/irc/resultlist/detailpage?id=3052421) and it shows the control linkages (there are two) located behind the hohenvergaser unit rather than attached to the front of it. Very confusing.
The Memorial Flight Association Fokker DVIIF has an original BMW IIIa but annoyingly among all the restoration photos they do not have one that clearly shows how these linkages are attached to the engine. However, they do show the radiator shutter linkage, which I shall add.