Setting valve lash on running motor

[Gusaroo]

OK, I've gone thru setting the valve lash on my hydraulic lifted. stamped rocker bbc with the engine off, but I am still getting a fairly loud tick from the passenger side. I replaced the header gasket just to be sure that wasn't it. So next I plan to try re-setting lash but this time with the engine running. I figured if I have a wiped out cam lobe, it might be noticeable. Ive watched a few videos and did some searches and it seems pretty idiot proof. Unfortunately I don't have an old pair of valve covers to cut up and I don't have any tappet plugs/caps so I'll just cover the valve train with rags or paper towels so as not to make a mess. My question...if I loosen the rocker till it chatters, then tighten down until it stops, am I done? or should I then set a preload? If so how much, 1/2 turn, 3/4 of a turn?

Any other best practices? or horror stories? Should I even attempt this?