It's a 10' foot long model made for the movie. The name Leper Colony comes from "12 o'clock high".
If you look carefully at the scenes of the flight over the Arctic, you'll see the shadow of the camera plane that shot the background. Unmistakeably a B-17.
"And they make such damn nice little cameras."
Sellars was to play Kong, even learned a Texas accent, until he broke his leg, which is why Dr. S is in a chair. The production sent a letter to John Wayne requesting he play Major Kong. They never heard back. Second choice was Dan Blocker, but couldn't reach terms. I think ole Slim was just the right guy. There's a rumor that when Kong completes the inventory of the survival kit and says "Fella could have a nice time in Vegas with this" he said "Dallas" but it was overdubbed in final production. (The movie came out in December 1963.)