1972 dart - stopped running while at 50 mph ? no warning

What does the spark at coil output look like? Is it good and blue and how long does it get?

Also, have you tried starting it with everything "normally" connected but with a jumper right to coil +?

Does the rotor look good? clean? Any sign of carbon through the middle to the shaft?

As clean as the cap / wiring looks I'm doubting that.