A couple comments, and a few questions

First of all, no steel loom on a stock CC 427 so this may be an aftermarket or Interceptor motor. You may be able to see some induction firing at night with the lights off, but if it ran well a while ago, this probably is not the issue.

I wonder if you have ignition points or Pertronix ignition. If you have points, or even the Pertronix, the rotor can still arc erode the inside terminals on the cap, so it's a "full motor search" for something like an intermittant miss like this.

You absolutely went to the first things I'd look at, being the wires and especially the valve adjustment. If your valve clearance redings are ok, then you eliminate the chance of a hardened seat coming out and causing one valve to stay open, and that would cause a major ticking in the motor of course.

A bad distributor cap could cause intermittant firing to the plug, I thought of fouling that may have been caused, or a wetted plug, faulty ignition wiring, loose ground, poor ground at the distributor itself. Not sure if a carb will cause a rythmic popping. Is it a regular rotational pop?

Try this. Just pull one plug wire at a time and run the motor. It will run just fine on 7 cylinders for a short while. If you have something going on in one particular cylinder thats causing a hiccup, this will isolate it becuase that cylinder won't be firing.

In the past I had a very odd backfire situation and I think a valve was so poorly adjusted, thanks to the previous owner, that the cylinder had zero compression. It was, however, breathing enough fuel vapor to really pop like hell once in a while, and I actually think some of the combustion may have been in the exhaust manifold area, not really sure, but in any case it REALLY got my attentiion around 2800RPM and sounded like a machine gun going off.

Please describe the exact nature of the popping, when it occurs, is it regular with the rotation of the motor or random, etc., and we'll enlist some others to also give you some tips.

Regards, Paul