The "Mushroom Cloud" design looked too humanoid -- more like one of the creatures in MATANGO, and not at all like a dinosaurian creature. Tsuburaya and his team liked to try and "evolve" their techniques and experiment as much as possible, which is why Godzilla looked different from film to film. Even in the 1990s films, where Godzilla is more uniform, there were subtle or overt changes made from film to film, which the average moviegoer would not necessarily pick up on.
August Ragone
kaijupro@yahoo.com