I've been researching this option for a dif too. Those '94 and earlier J30 difs have 5 bolt output shafts much like the 180sx dif I ended up grabbing.

But I do believe you will find that their installation into a s13 chassis is the same for the later J30 difs. That would mean its much like bolting an s14 dif into an s13. Both the J30 and s14 have a 2 rubber mounts in the front "ears" of the dif, where the s13 bolts directly, no rubber isolators. You will need to use your s13 rear cover because it 4 bolt, not 2 and front mounting bolts because they are longer...essentially the exact same thing as if you were using a '94 and earlier dif from a J30.

Here is some good info too: http://www.ka24development.com/vlsd.html

Consider yourself lucky not to have to have to source out different axles or output shafts. Though NAPA does have the 5 bolt axles for the cheap, as i was shown yesterday by NeedCAfors13.

Hope this helps and that others chime in to confirm.

-Royce