The 'S' Super6's only had LSD as an option. However they do have the larger BW80 diff centres same as the earlier VT1 5L's and later Gen3 V8's.
A quick way to check (provided no-one has tamperd already) is to look at the rear housing of the diff and under the oil filler plug there will be a tag. If it says HI PERFORMANCE then its only the BW80 NON LSD, but if that tag says says LSD then obviously it should be an LSD centre.
Also you can double check by raising the BOTH rear wheels clear of the ground together and turning them over by hand...if they both turn in the same direction its an LSD but if they turn in opposite directions its NON LSD.