Mercruiser 5.0 erratic clanking noise

I was idling my Mercruiser 5.0 305 last week in preparation of taking it out and suddenly heard an erratic clanking noise that I'm hoping you guys can help pinpoint. It goes on and off, and sometimes even becomes rapid (3rd video). In terms of maintenance, I've changed the oil + oil filter, fuel filter, thermostat, and coil wires throughout the span of a few weeks ago. The engine's probably idled for a total 40 mins while I've done all these tasks--can the constant idle cause this issue? I'm thinking the oil pressure is not getting to all the crevices and ports, and is starving a component of oil. Would putting the boat in the water and revving it for 30 secs - 1 min to 'clear out' the system be worthwhile to do?

Here are the three videos:

https://streamable.com/uel4h?fbclid=IwAR3xSn1CVMATBjdQZk4CFxu04ozF2t_lxq02NzPlvyF1xfj4JE4GPtbFX8A
https://streamable.com/9b4bs?fbclid=IwAR3xSn1CVMATBjdQZk4CFxu04ozF2t_lxq02NzPlvyF1xfj4JE4GPtbFX8A
https://streamable.com/xwngy?fbclid=IwAR0JUhWWScJYh5iUhrYPwVO7_EJG6IW6WH20hWkvVjukV8w4SjMzdUKQZUE

Thank you in advance!

Looks like all the rockers are moving okay (which is good--my first thought was a wiped cam lobe). Check your plug wires over carefully, to make sure you haven't any crossed wires. (Not sure how that could happen since it was running okay, but..) Then pull one wire at a time out of the distributor cap (use heavy gloves and insulated pliers) and see if there's any differences in power loss.

Jeff

Because the sound near the end of your crappy video, I would say look close for a broken valve spring. you may have to remove all the rockers to do so. Do you have or have access to a mechanics stethoscope? if so try to pinpoint the sound!!

Also...........................(way to much movement of the camera/phone, you should have focused on the location of the sound only)

I am diagnosing this issue with the OP and I admit the video is not the greatest. We will attempt to take better ones this coming weekend and try to focus on each cylinder individually. I poked around with a stethoscope and the sound seems to be louder when putting the probe on top of the intake manifold as opposed to putting the probe near the rocker and spring assembly. We don't have it on video, but we did have it idle for a good 3-4 minutes and noticed that oil was indeed running out of each of the push-rods onto each rockers and had good oil flow in the head.
I had heard from someone else that idling a boat may not be enough to pump sufficient oil through the entire engine and heads. We idled the boat for a total of 40 minutes the past month while diagnosing another issue. Could this extensive idling cause components to stick and result in the sound we are hearing? We are tempted to throw it in the water and see how it performs at higher RPMs, but wanted to get your inputs if whether it's too risky and if we should confirm some other things before we proceed with that.