the half shafts (hereby refered to as output shafts) are the same. Nissan uses a type of differential called an R200 in many of their models. The viscous unit is the same as an R200 except it has an added viscous coupler. Because of this, all output shafts can be swapped around in an R200 series diff. The catch is that the viscous units need a different length output than the open diff. This way, the outputs engage into the viscous coupler.
The main difference between an R200 output shaft is the companion flange. 240s use a 6 bolt, 3 pronged pattern. Silvias and 180s use the 5 bolt, 5 prong pattern, as do Z32s and J30s.
In short, as long as you get the output shafts with the diff, you'll be gravy (assuming that the diff is a US S13).
here's a link that will not only answer any more questions you have, but show you a step by step swap of someone installing an S13 V LSD into an S14:
http://importnut.net/lsdswap.htm