Possible oiling concerns

With the engine idling slowly you can run the feeler gauge between the valve tip and the rocker arm. Moving the feeler gauge in and out you will get a heavy drag when the gap is too tight and almost no drag when the gap is too large. And then you need to deal with turning the adjuster with it moving up and down.
I have had no problems with adjusting the valves with the engine warm, but not running.
I remove all six spark plugs, install a distributor cap that I have drilled out all six terminals on, so I can see the contact end of the rotor.
Then using a wrench to turn the motor with the bolt in the damper, turn the engine till the rotor points to #1 and adjust the # 1 intake and exhaust, turn the engine till the rotor points to the next cylinder to fire and adjust #5 intake and exhaust and continue in the firing order sequence.
Works for me.