I would take a tracing around the ring for the motor on a piece of aluminum
myself. I would guess that is what was done. Seems they would have the dimple in them if they went to the parts bin for the factory block off plate. Of course this is a guess. They do have a flat on one side. They are painted black so I couldn't tell if aluminum or steel by looking at it.
Being the entire car was engineered for lightweight it would make sense to use aluminum.
