Thanks for the replies!! Sorry, meant to update more information sooner.....

Motor started making this noise one day getting up on plane leaving the harbor.....

At the time of the video, which was last Friday. We had already broke the entire motor down (because we thought it was spun bearings), checked everything internal and all looked good except a bent push rod. Replaced that and reassembled with all new gaskets and plugs, etc etc.....Put the motor back in and the noise is still there......

Replaced the #6 spark plug wire, noise still there......

Swapped injectors, noise still there.....

No lack of power either......hope this helps

Thanks again for the ideas, hope one of them is it!

I would bet broken valve spring on #6.

yep,easy fix.

After listening again, I don't think the noise is consistent enough to be an exhaust leak. Valve train problems generally have a more consistent noise also.
I had a very similar noise on an SC'd SBC in a street rod. It ended up that the clearance was too tight on a wrist pin. There was no metal in the oil and no obvious damage until the wrist pin was removed.

when you say tore it down did you just pull the oil pan and look at the bearings?? its a sharp noise and sounds like either you broke a valve spring or one of the lifters may be slamming on the cam,,are all the dog bones for the lifters on correctly?
i remember on the gm trucks they had a distributor problem and would make a banging noise when the bushings wore out ..

Yes, took oil pan off.....everything looked good

thinking about basics,by removing plug wire while running, loading change is to wrist pin and rod bearing. also eliminates some exhaust pressure on that cycl. result from these changes.exhaust flapper,wrist pin,rod bearing. check and let us know,good luck

Would I be correct in assuming you did not remove the heads? That noise sounds to me like the piston is hitting the head. I suspect the piston is broken since it doesn't have a rod bearing piggybacked.

Heads came off, all checked out good unless we missed something? new head gaskets and reinstalled.........

Thanks to everyone for the replies!!

Sounds to me your exhaust valve is not opening all the way, and it is backfiring through the intake.

You mentioned a bent push rod, was it an exhaust valve rod? Chance that you siezed a valve and wiped a lobe off the cam?

Take the valve cover off and watch the rockers at idle.