The correct answer is C) By relying on resultant calculations from an inclining experiment. The final light ship weight, longitudinal and vertical centers of gravity, and final assignment of the load lines are determined through an inclining experiment. This is a well-established method in naval architecture, where the vessel is carefully ballasted and the resulting changes in heel and trim are measured to calculate the vessel's stability characteristics. The resultant calculations from the inclining experiment provide the necessary information to determine the final light ship weight, centers of gravity, and load line assignments. The other options are incorrect because A) relies solely on ballasting calculations without verifying through an experiment, B) relies only on design calculations without physical verification, and D) involves shifting ballast which is not the standard method for determining these parameters.