Honnestly the name doesn't ring a bell. I've found an article in french mentioning a driver named Roger Cohen in the 60's, but there's no mention to Ferrari or Porsche:
http://www.marcadier.com/histoire.htm
The only thing said about him:
L'auto fut ensuite munie d'une mécanique Renault 8 Gordini et cette voiture signa, en formule libre, quelques beaux résultats aux mains de Roger Cohen , le pilote attitré de la marque. Il remporta même des victoires au classement général, devant des monoplaces de Formule 3 !
In english it says: The car was then fitted with a Renault 8 Gordini engine, and it achieved some nice results in "formula (free?) libre", in the hands of Roger Cohen, the titular pilot of the manufacturer. He even won some races, ahed of some Formula 3 cars!
Note: the car in question is the ’Fournier-Marcadier'