Form and rules
How it works
Would + base verb often reports a future event viewed from a past point: I knew she would call.
Was/were going to expresses a past intention or prediction about a later event; the event may or may not have happened.
Was/were about to expresses something imminent at the past reference point.
Was/were due to or was/were to can describe scheduled or formal future-in-the-past arrangements.
Choose the structure according to the original future meaning, then shift the viewpoint into the past.