Is there a way in AutoCAD to assign mass properties (density) to various components and subcomponents to see what the center of gravity variations within a completed model are as each of the components are relocated? I seem to be unable to alter densities from one element to another. It appears that a single density is all I am able to use. Any ideas? Is Inventory a better option for this exercise?

Yes, Autodesk Inventor can do such assembly analysis.