Hard to know if it has an LSD if it's worn as Nissan seems to have fit them at random. If the orange LSD OIL ONLY tag is still on the back of your diff, there's your answer. If you jack a rear wheel up with the car in neutral and you can't turn it easily, you have an LSD and there's your answer. If no to both of these, get the rear wheels bogged in some nice slippery mud and stick it in gear and get out - if both wheels turn then you may have an LSD that is just worn out and needs shimming. The other option is to pull the diff centre (not that easy on a H233b diff, you have to pull the axles, you can't remove an inspection cover) and look at it.
If you definitely don't have one, you can fit an LSD centre from a 4x4 D21 (again fitted at random) if you find one on eBay or at the wreckers or something. You need to count splines etc as some are 31 spline axles and some are 33, so check yours first by pulling one of your axles out, then check the one you are looking at buying. Fitting a complete axle from a D22 most likely means you will lose your tall 4x2 diff ratio as there weren't any H233b-fitted (looks like a Ford 9") vehicles with the taller ratio that come to mind. If you change to a C200 (looks like a GM 10-bolt) where the ratios are available then you will have issues with tailshaft flanges, you can swap etc but it becomes a more involved project.
