ATI guys come in!
LS1 Fluid Damper
the ati pulley "sits" inside the crank pulley and uses the ribs on the crank pulley for support.
looking at the picture on the auction, the piece on the right runs the a/c and mounts up "behind" the piece on the left. in my case, the pulley for my sc mounts to the front of the dampner, the part on the left hand side.

