I bought a set of car body dollies from the same folks that made my rotisserie, it has two sets of interchangable uprights, one with u-shaped "cradles" on which you could set a rearend assembly (though the pinion snout would rotate down) and one with a pair of clamps that are made to attach to the rocker panel bottom pinch weld areas of a car body. So, If you buy this setup then you could also use it for a car dolly and not just something to wheel a rearend assembly around...
Or, you can just buy the setup that they make just for holding rearend assemblies, $150 plus shipping:
http://www.autotwirler.us/catalog/popup_image.php?pID=35\%27%29