Those are the magic words. The VG is a great engine, but it's not the best. Spend comparable amounts of money properly and safely tuning/modding a VG30 and an LS1. I guarantee you will massage more power out of the V8.
And like BryZ32TT said, getting a V8 into the Z is not a no-brainer. The few that have done it and written about it on this site have made that clear.