Those aluminum panels still have alot of filler and sanded spots in them. Making a finish suitable for just clear coating would be a tremendous task.
I saw this show on cable where they took a dodge charge and made a "bare metal finish". Essentially the care was prepped, sanded and clearcoated. It was beautiful! But a tremendous amount of work, as there could be no filler, no dings and no rough edges. Plus, when the body work was done, it had to be directionally sanded - like a DeLorean - before it was clearcoated.