Check for a bad cam chain guide before you get too far into changing the rockers as the slapping chain will sometimes mimic rocker noise. Those plastic guides are problematic. Front cover must come off to replace, but looking down from the cam gear and moving the guide lightly back and forth against the cam chain, any movement, replacement time. Get Metal replacements. 
I redid the top end 4 years ago But was under a deadline from the state of Colorado to get emissions and VIN check so I cut some corners. I know it's the rocker arms because when I did everything I put all new timing chain sprockets guides the work
