Thanks for your kind comments fellows.
Raven this is a very nice bird and a hell of a paintjob.
Greg: This cowling has given us all many hours of sheer pleasure, I see
Seriously, in retrospect I love these tough situations, they sharpen our skills.
What I did, since my cowling was painted final coat, I scrapped the interior surfaces graddually and test-fitting all the time, so as to create a 'step' on the back edge (like a locating bevel) and allow the assembly to 'float' when attached to the fuselage.
Then a coat of slow thick CA glue set it on place and the unavoidable misalignment was 'transferred' to the bottom of the join (some 0,5mm offset), where things are not so visible.
Yes, I admit I am a visual liar
Your result untill now by your method seems also excellent, I am looking forward to seeing it finalized & painted.