Any time your using aftermarket rockers, an aftermarket camshaft, hopefully milled heads and/or decked block you need to measure for correct fitting pushrods... Typically this is done with the engine mocked up, cam on the base circle, headgaskets in place, heads held by a couple bolts, rockers bolted down, adjusters centered in the oil groove, use an adjustable pushrod to measure he distance from the point of the adjuster where the pushrod normally contacts to the pushrod cup in the lifter without depressing the cup at all, with a hydraulic lifter you want to add .030 to the measurement for lifter preload..
