first up, ALL j30's had LSDs. they all have a 3.92 ratio.

u can find them on car-part.com

92-94 J30 axles you will need the J30 axles or output shafts from a 240sx with LSD (same R200v unit)

95-96 J30 will bolt in

lsd units will be 3/4 inch longer on the input snout that connects to the driveshaft. usually u can get by with mounting it because the worn mounts will have enough play. s13's will have to swap the diff covers in order to use the two bolt pattern to bolt it to the subframe.

http://www.intmo.com/briand/lsd.htm heres the whole piece. HTH

-dan