The assembly torque setting might not matter [except if too loose] if you're setting up a race-only differential, but for a street car rear you'll be better off to refer to the OE pinion nut spec for the one you're working on. Incorrect pinion nut torque leads to all kinds of gear/bearing noise as the bearing preload & gear backlash settings change over time. Typical pinion nut torque for a D-60 is about 250-275 ft-lbs. - a very "tight" setting, for a new assembly. However, if you are working with an existing differential setup the best approach is to measure the pinion rotating torque [prior to disassembly] and remenber to restore the setup to this rotating torque value after you remove the nut/replace the seal/replace the nut/torque it down. Experienced "rear" workers can sense the rotating pinion torque by their hands; other mechanics use an in-lb torque wrench to measure it. Both methods work well & will give you a better assembly!