In addition to what Captain Hook said, there can also be a low resistance path that shouldn't be there from contaminants (most likely anti-seize) on the outside of the coil, the wires or the dizzy cap.

For some reason, I didn't see the "still jmping fire from tower to the mount on the coil." That reminded me of the first tune-up I ever did myself way back when on my Olds Cutlass with the Olds 350 and early GM HEI system.

I had just learned that you're supposed to apply anti-seize to the spark plugs, but hadn't yet learned that you're supposed to apply a very small amount of anti-seize only to the threads of the spark plugs. I got anti-seize all over the plugs, the hex part, and some on the insulators, all over my hands, and from that all over the wires and the outside of the dizzy cap. When I started it after the "tune up" it was misfiring so bad it barely ran, and there was a huge crackling light show at the dizzy cap and a few lightning bolts coming down the outsides of some of the plug wires and shooting off to some bolt or metal bit on the engine. Learning is a process, and I caught on pretty quick, though. I was able to clean everything up and get it running smooth and strong again.

Since you can see arcing at the coil and coil wire, start with those. You might want to take the coil out to inspect it for contamination under good light, and to thoroughly clean it. Thoroughly clean the outside of the coil. Any spray household cleaner will work. Also a good time to get out the Ohm meter and check the coil, just to be sure. Use a Q-tip with cleaner to clean around and in the tower on the coil. Use the same cleaning routine on the high voltage coil wire to the dizzy.

When re-installing the coil wire, put a dab of dielectric grease in each post and in each boot on the wire. When you push it together, you've got the amount of dielectric grease "just right" if a very small amount oozes out at the ends of the boot just as you get the boot fully onto the post. If a lot oozes out, you used too much, just wipe away the excess. If none oozes out, push and squeeze a bit to make sure you're all the way on the connection, and it's your call if you open it and add more or leave it be. You want no "air space" at all in the joint. Any empty space inside the boot should be full of dielectric grease.

After cleaning the coil and coil wire, check for any arcing from the parts you cleaned. If that fixes the problem, contamination on the outside of the cap and wires is the most likely cause for arcing on the other cables. Also pull the cap and clean the rotor and inside the cap. Arcing in there is really bad, too.

Finally, I never saw an answer about the wire holders/separators. Are they present and in good condition? Those holders keep the wires from getting too close to each other and arcing across, and also keep them away from the metal bits on the engine, again preventing arcing issues along the path of the wire.