^I think I recall Godzilla showing up in an X-Men issue set in Japan. He fought Lockheed, IIRC. I thought at the time it was just a pop-culture joke, but I guess it must've been a crossover with Marvel's Godzilla comic.
It's interesting how Marvel treated most of its licensed tie-in properties as part of the overall Marvel Universe rather than separate realities. They folded in ROM, Micronauts, GI Joe, Transformers, Godzilla, even Jack Kirby's take on 2001. There was even a Marvel Star Trek comic in 1980 where a simulation of Marvel's Dracula appeared and Spock referenced characters from that comic as real historical figures.
I think that was actually Lockheed's female companion from the Beyonder's Battleworld. When the X-Men returned to Earth following the original Secret Wars they materialized in Japan. Lockheed's companion grew to enormous size in Earth's environment. If I remember right, at one point a couple of Japanese school children reference their "monster guide" to identify the creature and briefly consider it night be Godzilla beofre dismissing the thought.