Hi Stig,
I hope the headache passes quickly.
With regard to the id of the aircraft in the foreground, I believe I'm correct in saying the Lucien that answered earlier in the thread is Lucien Morareau, so we can regard the id as a Gourdou Leseurre GL.521 as definitive.
One must as the great american thinker E Cartman might put it "respect his authorotah"
Another image of the GL.521
http://www.airwar.ru/image/idop/bww1/gl521/gl521-1.jpg
Regards,
Clint