Used camshaft position sensor.  Cam sensor mounts in back of block.  Fits the following:

99-04 LS1/LS6 Corvette
99-02 LS1 Camaro Z28
99-02 LS1 Firebird/Trans Am
04 LS1 GTO
99-04 5.3L/6.0L LS Truck engines

The item in the photo is the exact item being sold.