engine noise

I totaly agree with Rustys extension=better than stethoscope.
Well now you have ruled out wristpins.
As to a cracked flex plate; in 45 years I only ever came across one.And I dont recall diagnosing it.However Im of the opinion that the sound would not be as difficult to locate as your sound is.
I know your antsy to get the intake off, but I wonder if......
Wait,I just thought of something; there is one last tin item inside the motor.Namely the oil flinger at the front of the crankshaft.And its in the chaincase. Which connects the top and bottom of the engine.I think I would check the torque on that ballancer bolt,first.Or at least sound out that case.And maybe the W/P as well.And while youre there maybe check the fan mounting bolts (JFTHOI); that theyre not too long and grinding on the waterpump nose.

Wait, forget that flinger business.I just reviewed the videos. I have heard this noise before. Give me a minute. Ill see if my brain can pull it in.Dont pull the intake just yet. Im sure the noise is in the oilpan.
No 6 rod bearing!Its not burned up.Its the wrong size shell.Or maybe #4. In any case Thats where Id be going.

Fellas; Anybody want to second that opinion.