i'm not a huge fan of those aluminum hold downs. they make it easy to distort the shafts since they clamp only a small area of the shaft.
when using studs on rocker shafts i use blue loctite to secure the stud to the head and green wick-n-lock on the nut. do not overtighten. call Harland Sharp and ask them about it.
the paper work that comes with the rockers should have the recommended torque.
you don't want to torque those down the same as you would for the same fastener in a different application. i would suggest no more than 30 ft. lbs. with 30 wt. oil. it would take 40-45 to stretch the stud and that will distort even a heavy wall shaft like you have. that's the reason i use the loc-tite.