First, just to clear any confusion, pushrod length does not change rocker geometry on shaft mounted rockers which have a fixed pivot point. Stud mounted rockers like on a Chevy are affected by pushrod length because this determines the height of the rockers pivot point.

Without modifying the rocker stands, the shaft mounted rockers can be raised with rocker shaft shims if the rockers are too low (or shorten the valve stem height.) If the rockers are too high, you could use valve stem lash caps or lengthen the valve stem height.

Pushrod length for hydraulic tappets should preload the lifter about 0.040" +/- 0.020".
This works for stamped rockers or adjustable rockers with the adjuster set correctly for clearance and oiling (depends on type of rocker/adjuster/pushrod ends used?)