C8 Z06s ordered without the aero package, will get at no extra cost 2 wickerbills. Sized just like the C7 Z06 corner wickerbills.
They will be shipped inside the trunk.

They attach just like the C7 Z06 corner wickerbills, specifically by first you taking out the roughly (4) 2” existing Torx screws on each side, and while leaving the black existing piece in place (it will not fall off when your car is parked due to its backside holders), take those screws and then go the existing black trim pieces, take the wickerbill you have in hand and then into the same holes (though the black existing piece), screw them in.
Every Corvette which has those wickerbills will have pictures and specific installation instructions.

The wickerbills have roughly 3/4” long but narrow ovals (screw diameter plus a little more) to allow you height adjustability and therefore differentially adjust your amounts of downforce.

At maximum extension, the wickerbill will stick up/out ¾ inch.