Mount them just like the front, same measurements for the mounts. You have a little movement in the drive shaft for it to lengthen or shorten when the cantilever suspension works, so you have room , but the best thing it to put the axle right back under the truck where it was. Bumper it there under the frame, brake line it right there, and no hassles. Look up xm381 on net, and look at the videos of the build. There is a guy on here that put them together and he is spot on with his measurements, and the pics are great. I have built 3, so pm me if you need to talk it out, and i will give you my # to call me when or if you get stuck.