You should have spacers between the upper and lower large steel washers. The spacer is what sets the load on the bushings, not the torque of the bolt. If there are no spacers I would look into getting them.
As for nyloc nuts the torque specs are the same. The nylon does not change the torque spec of the bolt to any large degree. Torque specs on 1/2 inch bolts is around 90 foot pounds.
