As I said when more information was available I would post it. Some understand the next paragraph. So for those who don't. When current is flowing through a wire there are magnetic lines of force that encircle the wire. The closer another wire is to the current carrying conductor the more the likely hood that those magnetic lines of force will induce current in the 2nd wire. We also can have voltage "leakage" where the insulator isn't sufficient and voltage can jump to the next wire. The last item that has been talked about is "flyback". An example of flyback would be when the circuit for the primary winding in the coil is opened its magnetic field collapses. This induces voltage in the secondary winding firing the plug. When this energy dissipates through the secondary winding it induces voltage back into the primary winding. This voltage is known as flyback. After talking to 6 electrical engineers I was directed by all of them to go and talk to the same person. This is what I learned from our EE PHD. As we've talked about having all the grounds in close proximity is a good idea. He was right on board with Monty's copper bar. He also liked the separate ground cable, but for a different reason. Running both a separate ground cable and the positive lead side by side helps cancel noise. That could be the same reason running the box leads to the battery was beneficial (leads side by side). His definition of what he thought would be the very best wiring.
#1 both hot and ground cables side by side.
#2 the hot cable directly to the starter, with feeds to a remote power stud and the alternator.
#3 the ground to the copper ground block.
#4 the block and heads grounded there.
#5 clean properly sized terminals and cable.
#6 twisted pair to sensors. with optional shielding grounded at one end
#7 care in running any sensor wiring near plug wires and or power cables.
Also note: shielding helps with voltage noise but doesn't do much for magnetic force.
In closing obviously in the majority of cases we get away with less. Make the choice of what you think you need for your application. I would think after reading this thread you can make an informed decision.
Doug