Thank you, everybody, especially for your opinions on the double turnbuckles. I will have indeed to verify the photos and decide which cables were so. However, for a moment my impression is, that all the lines, except for the u/c bracing, have two turnbuckles.
And tonight I managed to install the engine, connect its carbs by the throttle linkage, add the oil-breath pipe, the curved panel under the Spandau and build the cabane. The latter required some sanding in the upper part, because the connection to the upper wing centrepiece was far too tight - now the upper wing sits gently on it. The Spandau is put only provisionally to check the fit.



