Pushrods do not effect the amount of lift produced by the cam lobe. However, if the angles are off too far, the "effective lift" (as measured off the valve spring retainer) can be shrunk. The worse the angles, the less effective lift. Also, having things moving properly means less wear on parts, less oil use, and more power produced from that combination. When it's all said and done, you want the rocker's tip to be at 90° to the valve stem and centered at mid lift on the cam. To get this, you adjust the height of the rocker shafts with shims, or special shaft stands and retainers, or you change the pushrods. After a complete rebuild, things like decking the block and heads, different gaskets, different camshaft base circle diameters, valve jobs, and aftermarket part's specs all combine to change the factory pushrod length needs. Most times, shorter ones will be needed. Sometimes, longer ones are needed to keep the rockers' ajusters at a safe spot, or to keep hydraulic lifters preloaded properly. Pushrods are one of those things most guys take for granted and "assume" are fine. The right ones mean power and stability...The wrong ones mean it runs, and hopefully doesnt hurt anything else.
