It is my understanding that it was the 02 models only and they were done half way through the model year. It, if I remember correctly, is still an LS1 block, but w/ LS6 heads. And, I do recall that the way to find out is that the back of the engine head is stamped w/ "LS6." I almost certain it is behind the block on the drivers side. You have to use some good lighting and a mirror to see back there.
I'm sure on the location...99.99% sure on the model year, etc. But, take a look back there and see what you come up with!