9” drum brake retainer clips on assembly line, OEM?

Sounds like you are confusing things.
If you just want to remove the drum to inspect shoes, brake cylinder, and hardware; then remove the dust cap, cotter pin, stamped retainer, nut, washer, outer bearing and carefully slide the drum off. Be careful not to damage the inner grease seal. The drum comes off with the hub attached. No reason to worry about swedging anything. If the drum needs turning, it is done with the hub in place. Good time to repack the bearings and set preload.

Sounds like the other side has had the drum replaced in the last 50 yrs and the stud swedging was cut away. That drum could be removed leaving the hub on the spindle.

Now, if the drum is unusable and needs replacing, then most likely the swedging around each stud must be cut away and the hub and drum can be separated.

The clips shown in post #2 were only used to retain the drums on the car as it moved down the assembly line without wheels/tires. No reason to use them unless you are doing a true 100 point restoration. BTW, only 2 were used per drum, not 5.