Look on Differential housing
The easiest way to find out if you have limited slip is to crawl under the rear and look to the right side of the differential housing. There should be a tag there that says spezial oil if your rear end is LS if there isn't a tag it isn't.
"Tell me and I will listen, Teach me and I will learn, Show me and I will accomplish, Involve me and I will succeed."
'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan