I should redo this pic since I have better software. That said, the one in lower left has a Coanda nozzle:
The Beetle has, by my calculation, 1500CFM of engine cooling air in addition to the [corrosive] exhaust. A 4 into 1 or 4 into 2 into 1 header with a 90 degree elbow would feed into a concave stainless steel box with an insert to make it annular.
For drag, not anti-lift.