Rear U-bolts

Just trying to get the rear end completed and Ive checked the torque specs for the nuts on the u-bolts. I see they are 45 ft lbs. I have aftermarket from mancini and was wondering if they should still be at 45. Also they came with nuts only and no lock washers. Should I use lock washers or just the nuts. 45 doesnt seem that tight and I dont want them to loosen as I drive.
Also was wondering why such a low torque spec for that size thread. How does this effect the spring function?
Thanks
Rod