Based solely on the video, this does sound more like a lifter and less like exhaust. If the tapping does not start until the engine begins to warm up, that could mean when cold, the oil has sufficient viscosity to slow the bleed rate and add a bit more cushioning for that lifter. As the oil warms up and thins down, the symptom reveals itself. Not sure what viscosity oil you run. Most folks with bone-stock engines gravitate toward 10/40. Joe Gibbs offers a synthetic 15/50 that may help quiet that lifter down by slowing the bleed rate as the temp climbs. The ‘cold’ flow rate of a synthetic 15 wt shouldn’t be much different than the cold flow rate of a conventional 10 wt. This is not an alternative to a proper tear down / inspection / repair - but could help if a proper repair is not in the immediate budget.
FWIW - I had a 455 with one clacky HFT lifter after a full rebuild. No amt of adjusting cured it. But with Gibbs 15/50 synthetic, it was noticeably quieter than with any other oil I had tried. I honestly could have lived with it, but swapped in a set of USA Johnson Hylifts, and that solved the problem. Lifter faces and cam lobes were fine, but a couple lifters were bleeding down more quickly than the rest.
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