Many thanks for your encouraging and generous comments, Rick and Borsos!
I wanted to check whether the cowling will be ok, so I sprayed it with black Mr. Surfacer, polished it and gave it a semi translucent coat of Mr. Paint metalizer. So far I have not found a suitable method to render the "swirling" on the cowling to make it look believable in this scale. So for the time being I will just try to create the effect telling "this is not clean polished aluminium", therefore the translucency.
The wings and the tailplanes were given a coat of Drooling Bulldog zinc white and are ready for preshading. As usually I will be using Drooling Bulldog paints for the whole paintjob (fell in love with them). The fuselage and horizontal tailplanes will be painted with a mix of unbleached linen and umbraun lightened with zinc white, for the wings I will probably use the graugrün.
Cheers
Ondra