lifter preload

Make sure your lifter is on the back side of the lobe on your cam and tighten your rocker arm adjustment screw while spinning the pushrod in your fingers. Once you`ve reached the point where you can`t twist the pushrod with your fingers go about 1/2 turn more and hold the nut while tightening the set screw. That should give you ample preload with hydraulic lifters. As far as the shafts I would be more concerned with putting new rockers on old shafts than anything else.