Not sure why people claim the Donaldson Blackwing aircleaner cannot be used on a C6 other then some marketing hype from others but we installed one on a 2007 C6 along with our Team ZR-1 "ICEBOX"

After install customer went for a test run and was very happy with the performance and the sound of exhaust when using a freer flowing aircleaner and the colder aircharge to cylinders

Note : Customer bought the aircleaner and airbridge from WCC for $435 ! which we consider way high pricing and the airbridge is not designed very well.

Cutting the radiator shroud high at the top could cause air to swirl that can effect the MAF's output

Do not make a cut like the top image but correctly like the lower image with cut low and about 18 inches wide by about 2 inches tall.

Shroud is make of thin plastic so it cuts real easy.
Being the slot is hidden behind the Blackwing which is then hidden by the Icebox the cut does not have to be fine and square.