LS6 is a 5.7L just like the LS1, the main differences are revisions to the block (still 3.90 bore though), a cam change, the intake manifold and the 243 heads a few other things that I can’t remember too.
I’m 90% sure the throttle bodies are the same between the LS1 and 6 and I’m 99.99999% sure there was no “LS6” marking on the t/b of the Z06’s. Going on that, it looks like the p/o was a ricer and just threw that sticker on :lol
Talk to turbotravis or jammer or someone else who knows their shit in the LSx world