1969 frame cable gauges
A lot of these doors were put up before galvanized aircraft cable was standard, and even where it's been replaced once, the drums and safety cables on a 1969-era frame are often a different gauge than what's on the shelf for a newer door. The usual sign is a door that racks to one side as it closes, or a cable with visible rust bloom and broken strands near the bottom bracket where road salt and winter runoff collect.