I would look at the #4 cam bearing first to see if it is aligned properly on the top oil holes that feed the rocker arms
A quick messy way to check oil flow to the rocker arms before tearing into the motor is to prime the motor with all the spark plugs removed as well as both rocker arm shafts removed and spin the motor over on the starter while priming it to see if both oil holes out of the heads squirt the same amount of oil out of the heads
Let us know what you find