Back in the day with my 56 Chevys, I always used cold school copper wires. Solved a lot of issues. Thee is NO resistance with them babies. Lot's of EMI. Not good for radios, ECM's and modern phone hardware. (RFI). But on an old truck, who cares.
"Solid core" still used on high performance non computer vehicles.
The other type is carbon impregnated fiber core with a thick silicone insulating jacket. Look at the size of inner core and resistance/insulative value of the wire to determine what you need for what motor and ignition you have.
I wouldn't get too deep with this. Buy a preterminated set for 305 V6.
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