Hell, I noticed that when I first saw the movie, back in '88! I also noticed that the shot at the beginning, in Princess Nami's vision, was also lifted from Godzilla vs. Gigan. Though, with that one, they found a clever way to disguise the fact that it was a stock shot of Ghidorah blowing sh*t up.
"EVERYONE FORGET YOUR TROUBLES! ENJOY YOURSELVES!THERE'S NOTHING TO WORRY ABOUT!" - Gigantis The Fire Monster
"It was HUGE...It was...IT WAS LIKE A MONSTER!!! Suddenly the rocks rose...ALIVE!" - Godzilla 1985