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

Let's try it this way. You may not have hot enough spark. Jumper power to the coil direct. By the way do NOT leave this connected any longer than necessary than to make the test. If the engine fires and runs, you can leave it connected for a minute or two. This is hard on the coil and points

Now with the jumper connected, crank the engine by using a screwdriver between the two bare terminals on the starter relay, the "big stud" and the "big square" terminal"

Now you can see the spark and see how good or how bad it really is.

I am "assuming" this because you say "no spark at plugs." The rotor, cap and wires do not look too bad. The only thing left in that mix is the coil wire. You can check it (and the other wires) with an ohmeter