Cranks but doesn't start using the key. Starts when using a remote starter switch.
You said it was stock, with points, so the diagram is misleading. No power runs through the resistor during start when using points.
What you don't understand about 67Dart273's explanation is what you need to understand to trace the problem. On the back of the key switch is an I2 terminal and an S terminal.
The current path from the ignition switch to the coil is seperate from the current path from the ignition switch to the starter relay.
We know current is flowing from the S terminal on your key switch when the key is in start.
We know current is not making it to the coil wire J2B when the key is in start.
So the problem is in the Ignition 2 circuit. Whether its at a connector, a damaged wire, or in the key switch itself we do not know. But those are the places you have to look.