Are the rockers rail rockers ? looking at them on the 66 289 I don't like them they provide no lubrication to the valve stem. They do have a pin hole in the push rod socket to feed the ball but nothing to the stem.My thoughts are if the rails are contacting the hat on the spring as they travel could sound like lifter clatter. 

Although messy, try removing the valve covers and verify adequate oiling at low RPM.  Push down on each noisy rocker arm and if the noise clears up or reduces.   
A mechanics stethoscope may help pinpoint the bad performers, or where the noise is coming from (if not the lifters).
Maybe some debris is stuck in an oil passage not allowing full flow to the lifters? 

I would think this is related to oil pressure to the lifters.  One test I always perform before startup is to prime the oil pump with a strong drill and the valve covers off.  Watch for steady oozing of oil from the rocker arm at the top of the pushrod.  Defective lifters show either zero flow or an excessive amount, like a freely flowing faucet.  I have had new lifters recently exhibiting both issues. Gaba also had some new free-flowing ones. With all the diagnostics you have done, I figure you are way past that point, but still worth mentioning. 

Are you certain all the cam bearing oil holes are perfectly aligned with the supply holes in the block?  Off a little, they can block flow.

What are your clearances on main and rod bearings?  I shoot for 0.002” on mains and 0.015” on rods.  Too much and you start losing oil pressure.  I always check every journal on every build.

Then there is the weird stuff.   Just trying to think of anything that could cause noise.
Most likely not an issue since you have stock components, but check the baffles in the valve covers for rocker contact.  This usually gets noisier with rpm, not the other way around like yours.
Fuel pump eccentrics can cause noise with the fuel pump lever if an oil slinger was not installed on the crankshaft.
Any chance the rocker arms are contacting the valve spring or the head near the mounting bolt?
Pushrods dragging on hole through the head?

Run it for thirty minutes until fully warmed up and oil is circulating hot through the engine.  Vary the rpm. Cross fingers.  Get more powerful stereo?
I wish I could be there beside you for a forensic tear down to find the cause, but just too long of a walk.

Thanks for all the info.  Here is what I I have done in In relation to your suggestions

MS wrote:

I would think this is related to oil pressure to the lifters. One test I always perform before startup is to prime the oil pump with a strong drill and the valve covers off. Watch for steady oozing of oil from the rocker arm at the top of the pushrod. Defective lifters show either zero flow or an excessive amount, like a freely flowing faucet. I have had new lifters recently exhibiting both issues. Gaba also had some new free-flowing ones. With all the diagnostics you have done, I figure you are way past that point, but still worth mentioning.

That has been done twice, I did that when I originally put it together and I did it yesterday when I swapped the new lifters out for the old ones.

MS wrote:

Are you certain all the cam bearing oil holes are perfectly aligned with the supply holes in the block? Off a little, they can block flow.

What are your clearances on main and rod bearings? I shoot for 0.002” on mains and 0.015” on rods. Too much and you start losing oil pressure. I always check every journal on every build.

When I put in the cam bearings I was very carful to make sure everything lined up correctly and then I verified it with a flashlight.  As to the other bearing clearances I don't remember the exact numbers but I do know they were to the large side of being in spec.  There was some where on the crank and I used stock size bearings.  Like I said oil pressure is good at the gage and good when I primed with the drill.

MS wrote:

Then there is the weird stuff. Just trying to think of anything that could cause noise.
Most likely not an issue since you have stock components, but check the baffles in the valve covers for rocker contact. This usually gets noisier with rpm, not the other way around like yours.
Fuel pump eccentrics can cause noise with the fuel pump lever if an oil slinger was not installed on the crankshaft.
Any chance the rocker arms are contacting the valve spring or the head near the mounting bolt?
Pushrods dragging on hole through the head?

No baffle contact.  Fuel pump is electric. pushrods have lots of clearance.  I have not looked to see if the rockers are hitting the springs, I will check that.

MS wrote:

I wish I could be there beside you for a forensic tear down to find the cause, but just too long of a walk.

Me too, an extra set of eyes and ears would probably make all the difference.
 

Raymond_B wrote:

Yeah definitely valve train noise, or at it sounds like it to me. What is the oil pressure? Is it getting good oil up top? What do the top of the valves and rockers look like? Even wear?

Maybe go a tad bit tighter on valve adjustment?

Oil pressure is between 50 and 60.  Yes there is good oil up at the top and the valves look good.  As to the adjustment there isn't any other than shimming the rail.  I was getting the clatter even when the rockers were "tighter" before I shimmed them.  At that point the theory was there was too much preload due to the heads being milled.
 

I've always used a high-volume pump, not having your problem I really can't say it will help or not.
Something to watch out for ... on my 351W I have the dual-sump oil pan.  I found the high-volume pump was slightly hitting the lower side of the bottom of the pan (I never had this issue with a front sump pan), and did not realize this was happening until the pan cracked from the stress and was leaking.  Pulled the pan, a some hammer work and JB Weld fixed the problem.

BobE wrote:

This may not help Daze however it may help me.  When I primed my engine, I noticed one rocker had more flow than the others, didn't give it much thought  The engine has a slight ticking sound when running, that I couldn't figure out.  Now, I've got something to check.  Thanks.
 

I hope it fixes your issue so that all the time I have spent banging my head against this engine can be of benefit to somone even if its not me. 😂

 

Oil flow looks great.
Might just be me, but I would never have reused an old oil pump, especially in an engine with a known heat or bearing issue.
Perhaps it got hot enough to make the pressure relief valve spring not function correctly?   I know I have probably spent alot of money buying unneeded oil pumps through the years, but I can state I have never had an oil related problem in any engine I ever built.

I do not think your milled heads have anything to do with it since you have properly shimmed the rockers for proper adjustment.

Trust me, you don’t want a boat anchor or the boat that comes along with it.

I still stand by the idea a HV oil pump on a SBF  OR  SBC is a waste of time/money! If there is one thing these SB 'engines' do right its.......pump oil!

It ain't the lack of oil flow(watching your video).....Gotta be lifters/adjustment (somehow )
Do the suggestion of running it with the VC off and mashing/pressing on each rocker to see if the racket lessens.....

6sally6

M83HV

Raymond_B wrote:

You had mentioned earlier that oil pressure was 50-60, I am ASSuming that's not hot at idle? Is that at 1500 RPM and higher?

 
That’s all the time including when I primed it with the drill.

Greg B wrote:

Have you checked all the push rods for straightness?

yep strait as an arrow
 

Here’s hoping it cures the problem and you don’t wind up with something equal to my 29 years of trying to figure out where the 75 mph harmonic vibration in my fastback is coming from.

At least I know it is not my oil pump!