mellings pushrod for magnum heads?

The threads in the magnum head that holds the rocker pedestal on is a 5/16-18 thread. 18 threads per inch equats to 0.55" per revolution. Pick a cylinder and get the lifts on the base circle of the cam (both valves shut on compression). Slowly tighten the bolts while feeling the play in the push rod between the lifter. Once there is no more play and you can still rotate the push rod in your fingers tighten the bolt until the pedastel bolts on the head.

If the bolt rotates 1/2 revoltion then you have 1/2 of 0.055 or 0.027" of preload. More revolution is ore preload less is less.