318 cuts out when revving

74 dart sport said
We called pertronix about the coil and they said coils either work or don't work..

This is ABSOLUTELY not true

In FACT "classic" coil failure from "the old days" used to be that as a coil warmed up, it would miss, or fail, cool off, and "work better."

I've had at least two coils fail in this manner.