[Kenth]

I may be wrong, but "half lift" is lobe lift times rocker arm ratio divided in two is X.
Place rocker 90° to the valve stem.
Adjust the rocker nut half the amount of X.
Adjust the push rod for zero play.
(With hydraulic lifter add .050" to the final length of the pushrod)

To check, turn the crank, take measurement at valve tip for X and the rocker will be 90° to the valve stem.

Jobs done!