Tidbits:
I've never seen a reference to the Magnum getting the Road Wheel, de-chromed or not.
The XE got a special wheel, 'aluminum fascia' would be an appropriate name. The Magnum GT got a 15x7 version of the Super Coupe's 15x8 wheel, both were silver-painted.
The 79 300's wheel was indeed 15x6.