KAIJU (怪獣, kaijū) n. Japanese word loosely translated as "strange beast". Often used in English to mean "monster".
While not a "giant monster" movie per se, THE GREEN SLIME (1968 Japan/ 1969 US) was basically an American film produced in Japan. It's got Robert Horton, Luciana Paluzzi, and some pretty funky looking tentacled "aliens". It's also a fairly enjoyable film to watch, despite some of the aforementioned funky. And, be prepared for the UBER FUNKY theme song . . .
American Movie Poster
Italian Movie Poster
Robert Horton and Luciana Paluzzi (Above)
Various THE GREEN SLIME Lobby Cards (Below)