I have that written down somewhere but I can't find it....I had Betts Springs add another leaf to my rear springs a couple of years ago and they told me to check the torque on these nuts a couple hundred miles after they installed the new springs. Give them a call and they should be able to tell you:
Mine were made when I had the leafs reworked. I was given specific orders from the spring company to retorq them to 180 ft/lbs. These don't seem to be noticiably different from the ones that originally came with the SMB, so I'm guessing you'd be safe with 180.
It takes a village to raise an idiot.