No improvement. I can't see any arcing, but considering the strength of the shock I got, I'd bet arcing somewhere is the cause of the pinging. The pings only come out of the B bank exhaust.

 

Sounds like its time for a new distributor and plug leads?

 

If you got WHACKED, there be the issue.

As said:

New cap
New rotor, and do teh Mod.
New leads, all 14 of them, and good quality only.
New Spark Plugs, and gapped to 0.025".
Clean the throttle discs and throttle bodies, BOTH side.
Ensure the Disc to Bore is set at 0.002".
Reset the throttle rods.. BOTH side so they are balanced 100%, remembering that this is NOT a V12, it is a Double Six, so balance is critical.

That's the basics for this engine since 1976, when it went from Carby to Infected.
The Marelli, I know NOTHING, and love it. All I know is what I read in here, as can you.