When you pull the diff cover for inspection, you should be able to see inside of the differential, if you see clutch discs on the axle shaft side within the differential then it's a limited slip/posi/locking unit. If you see only gears then it's an open differential.

1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy