The original concept had more organic lines and smooth curves, looking much more like a blend of the Excelsior and Galaxy classes. The Memory Alpha article about the Ambassador class model explains that the final studio model was created by Greg Jein based on a design Rick Sternbach developed from the original concept painting and design sketches by Andrew Probert. Here is the original concept with a very different drive section/secondary hull that looks like a cross between the Galaxy and the Excelsior's drive sections: The Enterprise-C is an Ambassador class that is supposed to represent a transitional design bridging the Excelsior class and the Galaxy class.
