Grab a mirror and flashlight. look at the driver side, in the back above the transmission flange. if you see a 12561168 its ls6 block. Also you can tell by the block's luster if it dull in color you might have on or a dirty engine. 10-15% 01 f-body cars and 25% f-body cars have a ls6 block.
If you dont trust me. grad a camaro performers mag
fall 2003 page 83