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Ls2 and 3 are cast iron "log style" compared to the stainless tube, individual runners of the Z. The port match is not even close to optimum, but I'm guessing there is an overall benefit.
OEM Z06 manifolds and exhaust will flow much better than the OEM LS2/3 stuff.
Z06 exhaust is 3" pipes... LS2/LS3 is 2-1/2".
The exhaust parts are not compatible with each other, so if you are trying to use OEM Z manifolds, you will need the rest of the exhaust to go with it... IE Converters, mid pipe and over-axle/mufflers.
...FYI all the LS series engines use the same exhaust port layout and all the manifolds/headers will bolt right up, regardless of displacement.
The bolt patterns are generally the same, but the port size and shape is widely variable. The LS3 features a D shaped port that is not even close to the nearly round ports of the LS7. Consequently, there is a significant step when bolting the larger Z manifolds to the LS2/3 heads. They bolt up/seal fine, but the port mismatch is still there.