I'm looking for the two stainless or aluminum pieces that are on the rear quarter panels of a '59 Ford.

If your talking about the scuff plates or fender guards then I know on Packards and Fords those were stainless so I'll guess yours would be also.
I had to make a set for a Packard and I just rolled the top tightly to fit over a few clips and the lower body I just hand bent it to match the cars body contour. Then bent the bottom edge under the fender and screwed it down with two screws. They kept downward pessure on the peice so it held to the clips tight.
I then just gand trimmed it to fit the underside of the fender while it was still screwed to the car.
Most of those are screwed to the car at the bottom anyways.
You can buff up the stainless like a mirror. Just don't get any creases in it before you do.