Everything has to be together to measure the pushrods , the PRW at least include a tool , , gasket thickness , head or deck milling will all change the needed length . SO you get the heads bolted on & torqued down , turn the adjuster out 2 full turns from fully raised / top adjustment . then slide in a feeler gauge & measure the length of the pushrod between the lifter & adjuster nut if it is a solid cam or for hydraulic forget the feeler gauge & measure the length of the pushrod with the adjuster topped out & turn the adjuster nut down 2 turns to preload the lifter