OEM magnum lifters setup

What do you mean here? Half a turn on what?

The stock rockers should be tightened down all the way, all the time. torque to 21 ft lbs and done.

Yes I know pedestal type rockers should be tightened all the way down, but I backed it up to loosen the pushrod, tightened it to 21 ft lbs and it took about half a turn when I got it torqued and pushrod stopped turning at the same time. I think the stock pushrod must be a bit too short, maybe around 0.030'' like you found