Torsen or not?
 

I found a part out on Craigslist. Dude has a trans/ diff/ still bolted together w/ rear subframe/ shafts/ brakes/ wheels.
He said the car was a '99 S model. Trans is a 5speed, so I'm positive the diff has 4.30 gears, but torsen??

Ask the owner if it had leather seats or cruise control. It will be a Torsen.

Go take a look.

I was there yesterday, I bought a short block off him, but didn't have a whole lot of time to really look at the diff.

For a '99, a power antenna is another Torsen indicator.
Here is what to look for in the axle hole.
Differential Spotters Guide