the hicas vlsd, that comes stock in a select few s13s are direct bolt up but i was told that you need to swap driveshafts as well cause the diff is .75" longer, but i did it anyway.

you can also use the j30 vlsd. if im correct, the pre 1995 j30s came 5bolt, in which you would need the axles as well, but the 95+ j30s came 6bolt.

you can also use the lsd that is out of the z32 300zxs but only the N/A version.

eBay Motors: JDM Nissan Silvia S14 240SX 6 Bolt Rear VLSD Conversion (item 120203350754 end time Jan-03-08 19:13:06 PST)

if you look at the axles, where they bolt to the diff, you can see that there 6bolt and thats what you need cause s13s come stock 6bolt.