Carlos,
I have used a 12v Pertronix unit on a '54 Chevrolet truck for over 10 years and a 6v Pertronix unit on a '54 Chevrolet truck for over 7 years. Both with no problems. I use a Pertronix coil on the 12v system with no need for a ballast resistor.
Make sure you buy the unit that is appropriate for your truck (6v vs 12v).
