Then get a rag and fold it over a few times. With it running and that cover off, go down the line and push down on the pushrod side of each rocker hard until you can hear an audible difference in the noise. Then you've found the culprit rocker, pushrod, lifter, lobe. From there, you can disassemble that side and inspect everything. You should even be able to inspect that camshaft lobe through the cylinder head looking into the intake valley. You may have to turn the engine to inspect all of the cam lobe. I believe you can even get that lifter out with a long pair of needle nosed pliers. Just get that cam lobe up on the peak where it pushes the lifter up where you can grab it by the side.
