This modification ISN'T something you can do in your driveway, your axle tubes have to be precisely cut, and the ends welded on in a jig. You'll have to pull the rearend and take it to a chassis fabrication/performance shop to have it done.
Well worth the hassle though. No more leaking c-clip elim's, and you can run just about any aftermarket back brake set up, and it's stronger also....call Moser, they will hook you up with everything you need to do this correctly, and yes, you can get them in 4 lug.