I might be confused by the comments on this thread, but for the record, the caliper number is not a date code. It's the length (height actually) of the caliper leg. 500, 730, 890, 1080 are the common side pull sizes. This would denote the distance from the mounting pivot bolt to the center of the brake shoe adjustment.
More and more parts had manufacturing date codes added as product liability suits became more of a day-to-day occurrence.
Many, maybe most Maillard front and rear hubs had a date of manufacture code stamped in the middle of the hub. If no stamped date, it very early.
John