One armored car can carry a ton of gold. If they left and drove to the closest US Navy port, where the French ship would dock. it wouldn't raise eyebrows.
Based on some sibling discussion it seems it just never happened. It was multiple shipments, over many years, going over commercial liners. It may have well been armored trucks but they just didn’t all do it at once. It worked well that it didn’t create much of a media uproar.