The “two conductor” wire on the MarkII radios was a normal electrical wire with a braided sheath built into it to control RFI “radio buzz” caused by original spark plug wires. To elaborate, the original construction of a MarkII spark plug wire is it had a metal wire core covered with rubber insulation. Often times, this rubber sheath was not enough. Whenever 20,000 volts pulsed through the spark plug wire, it created its own field and would cause the radio to buzz which is known as radio frequency interference. How Continental dealt with this is adding a sheathed 2 conductor power wire which the inner core sent clean power to the speaker and the outer conductor simply carried stray RFI so it would not create static or white noise.
All speaker wires were back then was regular electrical wire but with a secondary sheath cast between the inner wire and the outer insulation on the positive side only. It wasn’t needed on the negative side because stray voltage would return to an earth ground before it would affect how the speaker worked.
That was the 50’s, here is what’s going on in 2021. Automotive speaker wire still is dual conductor and a specialty type wire instead of an electrical wire modified as an afterthought. Solid core wires also made an official mainstream exit during the 1990s and was replaced with the type of resistor/silicone wire that eliminates ignition RFI almost all by itself. That’s why modern spark plug wires don’t actually have wire in them, it’s carbon fibers.
More on spark plug wires: Barry posted a TSB some time ago concerning switching the positions of wires 8 and 6 in the spark plug wire brackets because they caused a misfire. This is true because 8 and 6 fired sequentially and the spark from wire 8 would often jump into wire 6 and vice versa. This needed to be done with solid core plug wires but is much less of a problem with modern resistance wires. I like running spark plug wires made for boat engines because they are built with better quality to prevent spark scatter and meet requirements to be used in a closed engine compartment with poor ventilation.
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