Some good high resolution under car photos of the 2,010 mile '71 Hemi Cuda here:

http://www.rkmotorscharlotte.com/sales/inventory/active_restoration/1971-Plymouth-Cuda/133269

Note that the sway bar, removable cross member piece under the trans, and the shocks are painted black also. The rear axle housing looks to be glossy black. This car has black painted springs. I think the brake backing plates are phosphated, not painted.