Help Me Diagnose My Miss

AJ/FormS said

Are you running a vacuum advance? And how is it plumbed? I have seen the Vcan pull the plate around and cause the spark to jump to the wrong tower. This happened to me. The cure for me was to re-index the reluctor and the rotor. You may wish to try running it with the can disconnected. You may have to rotate the distributor with the engine running,until it begins to run properly.
Or it could just be cracked insulators on a couple of plugs, due to detonation...........

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So I figured this out, kinda. I think a similar thing happened as described above. Turns out the ignition timing was advanced a LOT. I could barely see my 40* mark from the balancer on the timing cover, so there was probably around 50* advance at idle, causing it to run like ****. My only guess is that the reluctor phasing was off so much that the spark was jumping to the previous plug terminal, like what AJ was saying. How does this happen suddenly? And how do I ensure that doesn't happen again? Maybe the reluctor wheel slipped.