Hello,
I have just found your message. Indeed B17 #42-29937 of your uncle loss to a few kilometers from the airfield from Rennes St Jacques.
On the commune of Moigné.
I have had even for several months to recover photographs of the crash landing, according to a witness!
On the other hand I am supris that one of the engines is with the air warfare muesum in Nantes.
On the other hand a friend has at his place one of the pale of B17.
http://www.absa39-45.asso.fr/airfield/pertesusaaf.html
Dan