Bubba and others have posted tons of very helpful info. on the effects of using 1.5 or 3.00 or higher ohms coils along with ballast resisters and the data to show how coil resistance and ballast resistors influence performance on electronic ignitions. Just as a point of info. you can use 1.5 ohm coils with 12V. systems. I am doing so right now. Here's some info.
https://www.fordbarn.com/forum/showt...tributor+coils
It would seem logical to me that the manufacturer of Pertronix would know what's best for their products. Now, when it comes to Mallory electronic ignitions, I am not so sure.