That raised area is hollow, but as you can see, it's only raised about 1/4", so you have to be very careful drilling the holes.
The cooler lines they have now are either factory steel (which is how they were originally), or stainless (which is what the 69 T/A in the above photo looks like it has). There is some controversy about the clips, whether they should be black or natural metal. In the factory road tests and photos, the clips are natural metal, but I've seen many excellent restos where the clips were painted black.
