Aircraft cable drum systems
That gap matters for cables because doors from the early-to-mid 1970s were more often set up with galvanized aircraft cable on drum-style extension systems rather than the torsion-spring cable drums that became standard later in the decade. The two systems fail differently. A snapped cable on an older extension setup usually lets one side of the door drop hard and cock sideways in the track, because there's no torsion spring holding tension evenly across the top.