OK, I thought about this some more, take an ohmmeter and check your grounds to everything having to do with the holley setup. Try holley carb to frame, then holley to battery neg, then holley to base of dizzy. Try that same test you did except instead of touching the holley carb, ground the plate to the neg battery and slowly lower it but dont touch the wires, and dont you be touching anything grounded to car.... May get a jolt. Try it in the dark and see if you see any arcing.
How old are the plug wires?
I'm not saying the sniper couldn't be the main culprit, just trying to ID if that is the only bad piece in this puzzle. I'm also sure Holley will not want that video out....