marknbacon,
The way that rebuild on your 216 engine is described , it appears as a premium A+ "done everything a 216 could need" job. It seems very extensive (likely expensive) and worth bragging about that high level of engine work. But then the actual receipt and its itemization sure leave out
a whole lot of vital information.
Your posted video sounds (on my computer speakers) a bit like symptoms of "marbles in a beer can" detonation. BUT it is very hard to diagnose engine noise via video, so I would just be guessing the cause of the rattle/knock.
I advise that you keep checking all the simple stuff before you dig into that engine deeper. Eliminate the easy things to check. Look at the ignition distributor vacuum advance pot, see if it is moving on acceleration .Take distributor cap off and feel ign. rotor "snap" back on the centrifugal advance weights in the distributor. Hook a vacuum gauge to the intake manifold and observe the needle dance at various rpms (your video showed a weird disconnected line where maybe the vacuum wipers were connected?) . You already ran a basic check of valve tappet lash (I run that check with engine running @operating temp, low idle.) You can play with that ignition timing a bit more by advancing the degrees that are labeled on the little scale of the octane selector. Make sure your ignition point faces are clean, they can be coated with stuff when new. The compression test, power balance test from HRL ,and changing the motor mounts are all worthy efforts if you keep that engine.
Others here know more than me about that 6V or 12V ignition coil and the resistor , so perhaps they will add more....
All said, you are doing a great job of explaining the problem and actually trying to delve a solution. Get the simple test out of the way first.
I think a few of us may be reasonably suspecting valve timing, or cam stuff , or ??? ; maybe deeper issues that need a dial test indicator etc. Latter you could possibly pull off some engine side/pan covers and gaze at some engine internals ---- latter.
For now, keep it simple.
