Ah, thank you!! It is quite possible that it actually is Romeo Costantini then. Unfortunately, it doesn't look like Costantini is credited as an actor in any other films.
But is he the only unknown actor who appears in both Battaglie negli spazi stellari
and Anno zero - guerra nello spazio
? Because if it is, then it must be him!
EMANUELLE - PERCHÉ VIOLENZA ALLE DONNE? (1977)
QUEL MALEDETTO TRENO BLINDATO (1978)
RETURN OF THE SAINT, episode 19: "The Murder Cartel" (1979)
LA NOUVELLE MALLE DES INDES (1981)
I NUOVI BARBARI (1983)
And he must also be in DOTTOR JEKYLL E GENTILE SIGNORA because I recognize his face in some of the pictures posted here from this film!