Look for the plate sandwitched between the last two sections of the trans.
You may also want to check with German American Transaxle. They indicated to me that if you have the limited slip, the plate is unnecessary. http://www.germantransaxle.com
As for checking your box, have a look at the attached pic #21.
If we're talking about the plate style LSD from a 944 then that should reduce the likelihood of spider gears imploding obviously.... That's the primary benefit at least in my view. Have personally installed a number of these LSD's in 016 boxes and run pretty big hp/tq through them afterwards with no issues. But then again, I'm not a total monkey with the throttle and drop clutch starts.
The plate provides some much needed reinforcement to the rear of the cast iron housing, and that's helpful in all situations.