When were Magnum 500 style wheels first offered from the factory on Plymouths? I am pretty sure they were optional on '67 GTX. Did any come with the end of the line '66 Belvederes or Satellites?

Motor Wheel Corp. manufactured the "chrome styled road wheels" for Chrysler Corp. starting with model year 1967. Initially they were 14x5-1/2" for b-bodies & 14x6" for c-bodies. Motor Wheel Corp. manufactured similar wheels for GM & FoMoCo.

They also sold them aftermarket under the "MAGNUM 500" name.

They are in the "pocket salesman guides" as SALES CODE 580, look in the library at Hamtramck-Historical
code: 580 in '67-'68, W21 in '69, & W23 in '70-'78 maybe later.

Here's the '67 Plymouth b-body page:

Here's a recent post with some part numbers: Road Wheel Center Caps