The movie's joke closing statement read: "The director and the entire production sincerely thank the people and authorities of "The Island" for their courteous and generous collaboration during the shooting of this film, and they solemnly promise never to return nor to reveal to anyone the location of this last unspoiled paradise". "The Island" the movie was actually shot at was Key Biscayne in Florida, USA.
The World War II Japanese tank seen was not a real life WWII Japanese tank or replica, nor was it based on either. The tank was especially built for the film and was designed as some kind of generic tank but without any actual specific historical design.
Ironically, a line spoken at the end of this film by Terence Hill was not "Who finds a friend finds a treasure" but "Who loses a treasure finds a friend".
Terence Hill says the line "He who finds a friend finds a treasure" in the earlier Terence Hill-Bud Spencer movie Deux super flics (1977).