You're right... same short-block and intake manifold. The ls6 has different heads with D-shaped exhaust ports, sodium filled valves (on the '02), and better springs and retainers. I'm not sure if the pistons are different, does an SS have the same compression ratio. The Z has 10.5:1. Oh yeah the Z has a completely different cam, the '02 and up has one with an even higher lift.