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My last EK I gave up adjusting them but this EK I decided to really try to eliminate this , I had a nice EJ years ago that I DIDNT have all this !
So I renewed all the rocker arms bushes , this was great for a while until they loosened up again
On the Grey motors there is an oil bleed off hole in the centre of the rocker gear . In there day to adjust the Tappets with the motor running you had to clip a plate on to stop the hot oil splashing on you This is fine but with our older engines the oil presssure drops off at idle speeds and most of the oil comes out this bleed hole
So then I blocked off the oil drain hole this is under the hex. 'block' in the centre of the rockers gear
near where the oil feed pipe screws in , and beautiful , start the engine and watch as the rocker tubes all fill up
with oil , running down into the pushrod cups and cushioning all the applications of the rocker gear
But you have to have the thick black 'washers , either side of the hex. 'block'to seal in the oil
Now even with 008 & 012 thou clearances it sounds fine
Hope this is of help to y'all

That sounds like a clever solution.

I cheated and fitted a Nasco alloy rocker cover that's designed to reduce tappet noise

I think your idea is better

Prolly gain about 5psi oil pressure without that bleedoff

Had the same hole blocked off in my grey too

Another area that I found that causes a fair bit of noise is the camshaft profile. Some people maybe aware that camshafts (not all) have a opening and closing ramp profile machined on both sides of each lobe. These "ramps" are barely detectable by eye but do a vey important job in slowing down valve speed just prior to the valve closing and touching its seat. As grey motor cams are more about lift rather than duration (for good low end torque), they have a quite sharp lift rate (for their day!) which can cause the valves to smack their seats on closure. This produces a similar noise to tappet noise.
I have tried most cam places and queried them about redoing the ramp profile but its seems the advent of hydraulic lifters has negated the neccessity of having them anymore in camshaft design. In most cases I have had to take in an old Repco engine machining service manual to show them as they'd never heard of it!!
The good news is that I have discovered that some aftermarket cams with a mild increase in duration can improve tappet noise dramatically i.e. opening and closing the valve over a longer period and slower rate does reduce valve speed, valve seat impact, and subsequent tappet like noise.