They are all resting against the starting gate pin. That is, the spoiler comes to the very front of the body. Now when the car is at the starting gate, the starting gate pin rests against the spoiler and not against the wooden nose of the car. The spoiler can be quite narrow and made of some light metal - aluminum, sheet brass, etc. Supports could be posts made of heavy duty paper clip material.
Light weight is the key.
They may be illegal. They may be declared illegal on the spot because of the advantage they give. Check the local rules and check with the local rule makers before the construction - especially with the local rule makers. B. Make sure you know the height of the starting pin before you set the height of the spoiler. The front of the car is the front edge of the spoiler.