Need help with vibration

For what it's worth, after reading all the added information it sure does sound like an engine miss causing it.

If it were my engine I think the very first thing I might do is pop a timing light on all 8 wires and see if it' sees spark on them all.
The possibility of a cracked plug is there also, so even if a spark is going down a wire it doesn't mean it's actually making it across the plug gap.

I have also seen where the problem was actually just the plugs also.
Had an HEI customer that bought a kit and couldn't get his engine to run worth a crap and come to find out it was just the plugs all along.

With a cracked plug it can be really hard to tell which one it is unless you start pulling plug wires while it's running a find the one that makes no or very little difference when disconnected.
Of course you can find the wet plug also, but that requires pulling the plugs all out right after a shutdown.