No it has to be something on top of that.

What I mean is the way you calculated the box dimensions cannot work in AC. For AC the box dimensions are not the dimensions of a box that has the same inertias and mass as the car. This is what you calculated, a box(x,y,z) that weighs 1450 kg and has 2130,469,1738 inertias. AC does not want that as an input.

About the Dynamic Index, changing box width does not affect its value. Changing box length, box height and mass(wtf? it really shouldn't) affect its value. That means the DI we see in AC is based on mass and pitch inertia alone. Not yaw, not roll.