Luv's came with 4x4 starting in 79 from the factory (although there are a few older ones that were modified to 4x4 by an after market company before thery got sold) if your doing a SAS, there are two standards pretty much for the Isuzu crowd (Luv was made by Isuzu so thats how it applies) but the 2 most common swaps are Toyota Mini front end, and a Waganeer D44 (6 lugs, right width, and the diff is on the passenger side)
for more info on SAS stuff check out this site
http://www.4x4wire.com
do a search in the Isuzu Talk section, thats where your going to find most of the useful info there.
hope that helps ya