According to Dexter, the torque for the nuts on the shackle bolts is 50 ft lbs, not 80 ft lbs. Page #67, and the specs for
Shoulder Type Shackle Bolt with 7/16" threads.
https://www.dexteraxle.com/docs/defa....pdf?sfvrsn=42
I believe your rig does not have the wet bolts installed, and if not, this would be an excellent time to do the upgrade with the bronze bushings and the bolts with the zerks that can be greased. If you broke one shackle bolt, I would suspect all of them should be replaced.
http://www.morryde.com/products/70-h...le-upgrade-kit