It is assumed that lifter preload was correct,before any alteration. The only thing you have to worry about is how much preload you have. If the heads have been surfaced,or the heads have been changed,or the cam has been changed for a performance grind,the geometry also changes. In that case, time for new or adjustable pushrods. I went with the pushrod to fit method. I called Smith Bros.,and had them made to my spec. You can also deal with this issue by getting rid of the non adjustable rocker arms.