4 wheel disc help?

I'm glad you caught that, usually I make very certain I put Grand Cherokee to make sure nobody get confused, however I guess this time I failed.
Anyways these were from a 1995 Jeep Grand Cherokee with rear disks (obviously).

I don't know which is lighter, but I would think the disks are, especially how I run them (I trimmed the excess knobs, brackets, dustshields, and am not using a parking brake set-up).
I would think spinning that small rotor has to be easier than turning a good (large diameter & thick) brake drum (think rotating mass).

This is my mock up to make sure everything was going to actually work out: