I have watched your thread and thought about some of the demons I have chased over time and here is a pretty good way to eliminate your valve train.
Get some old towels, unbolt both valve covers, lay towels around your heads and not on your headers so as to catch any
oil that may splash off your rocker arms. Start your engine and walk around and remove each valve cover and observe each lifter and listen for any noise. After you pull the valve covers off one side and check it out set the valve cover back on ad do the other side. If you still cannot pin point the noise. Drain your
oil and pull your
oil pan and take a look at your bearings the noise could be a loose main or rod bearing. I had a spun main bearing last spring that sounded like a bad lifter.
Good luck.
Clois Harlan