Heres a short cut I learned that will get you in the area. Take a sharpie and mark the top of the valve. Place the rocker on and adjust the lash. now rotate the engine over a few times opening and closing that valve. Then take the rocker off and check the mark you made with the sharpie. The rocker would wear some of the marking off and if that area is pefectly in the center of the valve its the right pushrod length. If not adjust the pushrod length checker until you do.
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