Peter,
Regarding the "later" wheel covers.
There is an early-late wheel cover made of chrome plated steel, and a later-late wheel cover (current production) made of polished stainless. As astute observer can tell the difference because polished stainless, no matter how well polished, has a different color than chrome. Then, of course, if the OEM steel wheel cover has been in any kind of use, there is probably rust on the back of it.
I know of two different kinds of clips to hold them onto the wheel. The first is a plain, zinc-chromate plated steel; the second is identical but it has these little plastic bumpers on them to protect the wheel's finish.
I have pix of the later style covers, and both kinds of clips, too. I don't know if I have the chrome-steel covers any longer.
Michael Salemi
1969 280SL
Signal Red 568G w/Black Leather (Restored)
President, International Stars Section
Mercedes-Benz Club of America