Are all S13 diffs LSD's?

[jonnyjapanese]

On the diagram you posted showing the S13 inners into S12 casing you used the drivers side inner cup from the S13 would using the S12 original drive shaft work if the splines were machined to take the circlip and maybe shortened or do you definately have to use a short passenger side S12 drive shaft onto the drivers side, the best bit is both my drive shafts measure 10" so which is the short one????