Interested to see pictures of this feature. I only know the single Malibu-style baffle of hard (now brittle) plastic that bolts onto the bottom the rad support. I took mine off and pitched it years ago since it had been massaged by some parking bumpers over the years. I found a decent used urethane SS air dam that probably makes the deflector OBE. Anybody know if was the case with El Camino SS - no deflector if you have the air dam from the factory?
A Bumper mounted air dam doesn't really help radiator cooling like a core support Air Dam would.
The purpose of the core support air dam is to make a lower pressure area behind the radiator when moving. A bumper mounted airdam can make a lower pressure area in front of the radiator
On a street car, bottom feeding the radiator (under the bumper) is a good strategy. On a 200 mph race car mixing it up with a pack of cars, this is bad idea, but keep it below 180 mph and don't draft anybody, getting all of the air below the grille and it will be fine.
Even with a deep airdam, unless the car cannot drive over a speed bump with out the airdam hitting, there is enough gap than a core support airdam will help cooling.