OK, now it's certain! Giovanni Forti Rosselli does indeed play the young curly man (François Roussel is the name of the character, at least in the English-dubbed version)!
He acted in a few more films as "Giovanni Rosselli". One of these films was the mythical rock-opera Orfeo 9
(1973). Here are a few pics of him from this great film - he is clearly the same as the young man in Chi l'ha vista morire
The question that still remains, however, is if Giovanni Forti Rosselli the actor is the same person as Giovanni Forti Rosselli the journalist. To me, it sounds very probable that it's the same man but it's impossible to say for sure. I reckon that someone
must know, though...