Looks good Patrick, I also am keen to see your finished model.
In 1998 I did a similar project in Autocad (2D) on the Mercedes engine. From that project I produced a book of drawings for the engine (ISBN: 0-646-35145-1) and built a 1/5 scale model; see
http://www.wwi-models.org/Images/Butler/index.html.
The model got no further than the images on the web site above, although I plan further development. More work is needed on the cylinder jackets and I have not yet made the patterns for the inlet manifold and carburettor. At present there is no need for me to create a crank case for the 1/5 scale model because the plan was to develop a replica engine to fit into a flying model. Part of the future development is to achieve some serious weight saving.
I also intend to create a 3D version to fit into my 3D airplanes (Pfalz D.IIIa will be first) and that project is likely to happen much sooner than an updated 1/5 scale model.
Regards
Paul