Hello
The collaboration of French Industry and German one in the 1941-1944 years is no secret at all :A great part can be found in
" JANE'S ALL THE WORLD AIRCRAFT 1945 " p 93c to 95c
Those infos were partially published (with the very same words!)in Kens -Nowarra book of the early 60' and in Luft 46.
quote :
"""" In December 1944 the French Air Ministry presented a comprehensive picture of the aircraft industry activities during the four years of occupation:
............... .....................................................
.............Fw 190 :THE BRANDT FACTORY at Chatillon sur Bagneux was requisitioned and put onto series production of motor cowlings for the Fw 190.
This plant was also alloted to the " Groupe Technique de Chatillon " as a prototype factory .It comprised some 300 French designers & engineers under the strict tutelage of technicians of Focke-Wulf. They studied Fw206 ,Fw 300 ,Ta400 .... """"

By the way the collaboration continued after a break of one year ,and as soon as in the late summer 1945 many German designers & engineers were working in Germany and in France with more (ATAR ) or less (Focke...) success .
The production of German planes continued for some pretty long after the War:Ju 52,Ar 396,Si204,Do 24 Me 108,Me 208,He 274,BV 144,Fw 190,Fi 156.