Intermittent Ignition Issue [66 Valiant /6]

Actually I think the crank contacts in the ignition switch is worn out.

Turn on the key and short across those two contacts.
Car should start and run.
You are very likely right, TB OP your start relay will not have the one at top left in the diagram, and the the one below the stud will be what I call lthe "square screw" terminal. There are only two exposed relay terminals. The "big stud" which goes to the battery, and the "square screw" and that leads down to the starter solenoid.