Have seen but I wouldn't do it that way
I like using a grease pencil
Remove all the plugs. Back all rocker nuts out so their either nuts are loose, or the rocker nut is at the top of the stud.
Rotate motor 1/2 turn.
Look for any rocker which is down opening a valve. Go to valve next to it in same cylinder which is full up. With fingers on one hand, grab the push rod. You should be able to rotate it back N forth and up/down.
Start tightening the rock nut down slowly with one hand, while your other hand is moving the push rod up and down. Being able to rotate push rod is good to make sure it stays centered in lifter and rocker.
What you want to note is when the up and down movement stops. Once the up and down stops, the push rod will still be able to be rotated, but this means next to nothing. Its the up/down that is important.
Once all up/down stops, this is zero lash point. Now rotate the nut one full turn down (Clockwise to right) more and your done. Mark rocker with grease pencil and go to next rocker.
Do this until there are no others to do. Rotate the motor crankshaft another 1/2 turn noting which ones go down and up.
Repeat for each rocker, and rotate as need to make sure all have been done
