Are the Dana 44 and Dana 60 rears only for the front?? Or can you get them for the back as well? I see everyone talking about a 14bff rear as the toughest out there to put in the back, is this a Dana rear or a GM corporate rear?? What is the diff between a sff and bff rear? I've searched and come up with the fact that the bff has external "hub" type setups out back, but what exactly does that allow for?? Thanks for your help! I'm a definite noob to the truck world!