Looking at the new "testing" pics closely, I believe the cheap looking hood is hiding a hood. I'm definately thinking Z28. Why not hide the Z28 by making it look like the ZL1 as much as possible? Also it looks like a mesh in the what would be brake cooling duct area. Plus where is the ZL1's side aero? Testing the Z28 could take another year plus putting it out far after the ZL1's huge "entry" has passed.
Chevy has to keep the excitement comin'! So I do believe this is a Z28.