Those are C5 exhaust manifolds. Its an LS1, 99-04. Can't tell if theres an EGR port on the top of the intake or not. If so, its an LS1 intake, meaning that its Pre-2001. I'd guess 853 or 241 heads.
Either way, it will be a great motor for a Z!
The swap can be done for a reasonable price, but don't get carried away with the "while I'm in there" stuff...... ask me how I know.