i've been driving v-8 rwd vehicles in the winter since getting my license. From my expierience, having both rear wheels driving the vehicle is a mixed blessing. It helps you alot to get started at a stop sign or intersection but on the highway hitting a patch of ice on a limited slip/spool is going to bring the ass around quicker than anything.
On the other hand, kit is a pain in the ass trying to get 1 wheel to get you going from a stop in heavy snow, but on the highway when you hit a patch of ice, the drive wheel will break traction and the left/dead one will help to keep the rear strieght.
if the truck already has a limited slip and you weld it up, you will make it worse.