Dexos 2 is the certification for Diesel engines. You want Dexos 1 for your C7. This site lists the current Dexos 1 approved oils.I believe it says Dexos 2 aproved oil for the Z06 C7 - ??? and a 5W30 or for track 15W50?? is this the correct??
dexos1? Gen 2 Brands | GM dexos® Licensing Program
Yes, 5W-30 for street use, 15W-50 for the track.