What, if any are the hole configuration that is drilled in the steel reinforcement plate. What are the number of holes, and center to center across, and center to center front to back. To get the center to center measurement, measure from the front edge of the first hole to the front edge of the second hole. If the holes are not evenly spaced front to back, then a diagonal measurement will also help. This will help to identify the base that was used, and give you the correct series of siren that originally came mounted to the car. If there are no holes, that would indicate that it was ordered with the reinforcement, but a mechanical siren was never installed on the roof.