Stock Rocker arms clearances and fit

I'd figure out which valve or valves are making the noise. Bring the engine up to normal operating temp so it will idle at a low RPM, pull the valve cover, fire it up, and see which valve is making the noise. You can run a .010-.020 feeler gauge between each rocker tip and valve stem to determine that. With the feeler gauge in between the rocker and valve, the noisy one should quiet down. Once you find the offending one, pull the rocker assembly and check it's individual rocker and push rod for wear. If you're lucky it might be one where you can also pull the lifter out with a magnet. If the rocker, push rod, and lifter don't have any wear, maybe the valving in the lifter is bad. Push the center cup of the lifter with a push rod and see if it moves easily. If it does, I'd replace it. If everything looks good, it may be the wrong length push rod. As mentioned, when the lifter is pumped up, there should be no free clearance between the rocker tip and the valve stem with the cam on it's heal for that cylinder.