Tom, you got two completely different engines here. Look at a Corvette forum to see the LT numbers on the Z06,they will be pretty close. The Z has a pretty we'll designed exhaust system on it and may not benefit as much as a Z06.
As for LTs on a 6.2 you can expect about 20 HP by themselves and more if you add a Better Cat-back system.
Where are you and are you prepared for modifications to your system that won't allow you to just bolt OE back on if needed?