Ace of Cakes just aired a show with a cake like this for a young man's Bar Mitzvah. I'm going to assume that you don't have some of the equipment they do (ie: welding etc.), but the principles stay the same.
I'm think a wonder mold pan for Kong's body, wooden dowel inserted into a base cake as Kong's spine, floral wire (heavier gauger for required support) wrapped & shaped around the dowel as the arms, covered with fondant or modeling clay (or make the arms in gumpaste a couple days ahead to allow for dry time - breakage risk though). Rice Krispies for the head and covered with fondant or modeling clay.
In the show they did a small character of the boy (fondant) place in Kong's hand. Not so sure if this helps, I usually draw a schematic image of a cake before attempting. It's easier to catch things that may not work out that way. Good luck and remember to post an image of your completed cake - love to see it!
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