My guess is the civil war in Congo forced their hand in shying away from using "Terror in the Congo". The war broke out in '97, right around the time KD would have been putting the ride marketing together.
What a shame that show never came into fruition. It sounds spectacular. (Although I suppose it all would have been lost now, anyways...).
Also, this is further evidence that the park did originally plan for the enormous Lost World waterfall to be used for Volcano too. Again, a shame it was never used, but it would all be in the past at this point.
Those were added in early July. They used to be in the queue and now they're on the path so guests can still play the Volcano character in the game (but does anyone actually?). Here's a picture of the one by Scrambler.