Part number is in teh "common part number" thread. Add Dorman in front of what Matt said.

All Series 2 motors from 96-99 had a tensioner with a lower elbow case as part of it. W bodies got a different alternator in 99 that took a different tensioner the other body styles swapped over in 2000.

The reasoning behind no longer having the elbow as part of the tensioner is because when pulling on the tensioner to remove it, people were breaking their timing covers.