OK, you made me go and research some more.
All LS1 (V8) and Y87 (V6) Firebirds received a Zexel/Torsen II slip-reduction rear axle. So it is 'included' basically with the G80 AXLE,REAR,POSITRACTION,LIMITED SLIP POSITRACTION L/SLIP R/AXLE option.
Also looks like it is not in that registry in your link.
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John Wallace - johnta1
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