newowner,
There is no correct wheel for a CS, they follow what ever the correct wheel is for a 68 Mustang. If you got the "GT" package along with the "CS" option, remember just because it says "GT/CS" does not make it a GT, so if you got the GT option you have the slotted wheels. The correct slotted wheels for the GT are argent or silver, you could get them changed for the chrome wheels. The center caps for a GT optioned car do have the "GT" in the center. Now if you did not get the GT option you could buy the chrome wheels (not argent). The center caps for these are plain.
Doug