Tim Smyth wrote:
I believe that he wanted to make a film about gorillas, or a gorilla, and film on Komodo island,

Yes. As I stated this is mentioned in the book. On page 186 there is a excerpt from a letter dated June 19 1931 (months before he went to RKO or saw Creation) that he written to Selznick (he became friends with Selznick back in the 20's when he was working on The Four Feathers) where he stated:

I talked with Paramount about the possibilites about making my gorilla picture for them and to tell you the truth that is what I'm personally very anxious to do. I really have a great idea along this line and if you think any of the companies would be interested or that Myron could get one of them interested I, on my part, would be delighted if you would let me know.
  
Cooper also stated in letters to his lawyer (when he was fighting RKO over the rights to the character) that he created Kong "long before I came to RKO". (page 362).

I just don't think that the gorilla was supposed to be gigantic, and later, at RKO, it turned into the Giant Terror Gorilla. There has never been one piece of paper, or outline, or even something scribbled on a napkin, referring to Cooper's original concept. Willis O'Brien made giant monster movies, and even had a Kong looking  missing link fighting fighting a dinosaur in 1916. My guess is all this gelled when Cooper saw the creation reel,  then the painting, maybe because of a misconception of the word huge, or giant, and Kong was born.  His explanation of filming on Komodo island and making the creatures appear gigantic also doesn't  make sense to me.  Cooper made natural dramas, OB made films of the fantastic, together they made the greatest fantasy movie ever, that part I am sure of.


Its entirely possible. 
What's been written about the "giantness" of his gorilla is that Cooper envisioned his "terror gorilla" being a giant when he visualized him on top of the tallest building in the World fighting warplanes. Its been stated in the book, The Making of King Kong, that Cooper came up with that sequence before any other part of the story. He essentially came up with the ending first and pieced the story together backwards from that. (pages 37-38)

In Dangerously, (pages 186-187) it states: The Monstrous gorilla had been gestating in Cooper's imagination since 1929, but after John Hambelton's death Cooper had focused on the emerging storyline with a new passion. And in February 1930, when he was leaving his midtown office, heard an engine overhead, and looked up as an airplane, gleaming in the setting sun, passed over the New York Insurance Building. "Without any conscious effort or thought I immediately saw in my minds eye a giant gorilla on top of the building." (This is also mentioned in David O. Selznick's Hollywood (pages 76-77).

If Cooper envisioned his terror gorilla on top of a building fighting warplanes, it would make sense to make his gorilla enlarged for such a battle to take place. Pitting warplanes against a 5-6 foot gorilla doesn't have much merit.

I understand that Cooper did "docudramas" but he was a man that was fascinated by larger than life characters and fantasy so for him to want to shift his "terror gorilla" story from docudrama to fantasy seems very plausible.

The Catch of the Day!