1992 Ford Ranger looking to convert to posi-trac! What's the best way to go?

My '92 is slow as crap and I'm doing a major overhaul with it. I'm already looking for a 302, a 351W, or a 5.0 Mustang Engine to replace that sluggish and torque lacking 2.3 liter 4 cylinder, but I also want a Positive Traction rear end! Now I know there are many ways to do this, such as P/T kits, or getting the rear end out of an Explorer or a Bronco II, but which is the best? Please Help!!!! Also, how hard would it be to change it over to being 4X4? Like getting the components i need out of another ranger 4X4 with a blown engine or something and putting them in my Ranger to convert it to 4 wheel drive???