Now I'm back and I can explain.
While I was looking for info about Dagonet, I saw in the same page the Cousy.
I knew I saw this puzzle car and I remember it was something like that (the Cousy in that page is a streamlined racer too, not like the 500 racer).
When looking in my HD for Cousy, I remember also this De Coucy.
The rest can be easily found in the net:
De Coucy Longchamp, 350cc from 1953.