Souplex was a Belgian brand of motor cycles that existed between 1939 and 1945. This was their marque. Quite beautiful. Even more so when surrounded by the rusting paint of the bike’s frame. Perfect colour harmony. Sorry you dont’t get to see the vehicle though- i’m a designer not an engineer!  Spotted at Les Puces de Saint-Ouen at the Porte de Clignancourt. It may still be there. Go and have a look. A brilliant place for inspiration.