All years and models should have the metal plate held to the subframe by 4 bolts. The plate is painted dull black.
A car should not be moved unless both plate covers are in place Moving a car with a missing cover allows the subframe to move.
If the mount moves, the car must be lifted to or jacked up to take all weight off the mount to allow the plate bolt holes to align correctly.
The 230's and early 250's had a plastic cover over each plate. These were eliminated in the later cars. 280's did not have the plastic covers.
Richard M, NYC