I would recommend 2 things for the lsd.... and neither of them is the tire spin method as this has been discussed as not quite right before by people who know....
There should be a sticker on the diff itself... it will indicate R200V or VLSD.
Not the vin, but the model number posted near the vin on the firewall..... here is a link to the check
http://socal240sx.com/faq/specifications.html
and
http://www.nissaninfiniticlub....+VLSD
[edit..... this wheel spinning method may work, but with all the dicussion on the matter, I would just assume use another method]