Scanned some pictures from the manga. Phew! The manga is basically a scene by scene remake from the original film that has a few differences here and there. The manga starts off with Gamera killing Legion and flying off into the sky. Meanwhile, three treasure hunters, Keisuke, Onodera, and Ichiro (who is now missing an eye instead of having a limp) set off to New Guinea to find the opal somewhere in Rainbow Valley.
Finding a cave, they go inside only to find dozens of rotting corpses and the bones of a mysterious creature.
Finding dozens of tiny rubies, Keisuke looks up at the skeleton, and what appears to be a tear-drop, comes falling down into the group.
Onodera quickly snatches the prize opal and gets in a fight with Ichiro. After receiving a nasty cut from a machete, Onodera shoots Ichiro in the face and the entire cave begins to flood drowning Keisuke while Onodera makes it out in the nick of time.
When Onodera comes out of the cavern entrance, he is met by a bunch of pissed off natives with shotguns and machetes. He runs
Raiders of the Lost Ark style back to his plane and flies off, leaving Keisuke floating in the water dreaming about demons.
Give me some more time and I'll have more scanned.