[Rev]

I checked my '66 shop manual for valve adjustment procedure on the 6 cylinder engines. It shows a non ajustable rocker arm and says to use oversized or undersized push rods to get the proper preload on the hydraulic lifter.

Since your engine does have adjustable rocker arms, you should be able to get the correct preload with the rocker arm adjustment.

The easiest way in my opinion is to rotate the crank until an intake valve is fully opened and then adjust the exhaust valve for that same cylinder. Then do the same to open the exhaust valve and then adjust the intake valve. All you're really doing is making sure the valve that you're adjusting is completely closed. It sounds like you adjusted the valves with no preload at all. That would cause valve train noise. I would take up all the slack, rotateing the push rod with your fingers as you tighten the adjustment down. When you feel resistance to rotateing the push rod that means all the slack is gone. Just give the adjustment another 1/2 turn to preload the lifter, putting the hydraulic lifter piston about in the middle of its travel.

After you do that to all the valves, you shouldn't have the valve train noise that you are experiencing. You do all this on a cold non running engine. No burned fingers, hot oil shooting all over everywhere or any of that. Try this and see if it doesn't work well for you.

Rev