After reading your post, I was curious also. So I tried to find out. Apparently there is no single answer. Variables such as which brakes are used, which style posi unit you've got (or spool), and even which housing you've got each go into determining the weight. The general consensus from what I've read is that the Dana will likely be 30 to 60 pounds heavier than the 8&3/4. But I've also read that the Dana is supposed to be a more efficient design that is supposed to negate the added weight. I found this thread on Moparts where it's being discussed: