Danny,
The grills have lugs that sit in plastic grommets. The problem is that over the years the plastic hardens and the grilles become difficult to remove and as they are cast Al they have a tendency to break. It's difficult as prying under them may chip the paint (unless you are in restore mode and its not so important). Maybe you can feed a wide webbed belt through the slats at one end, up in the middle and back to the other end allowing you to pull evenly in three points.
The vandors sell replacement grilles without the wiper shaft holes for a clean look if you so desire.
Julian
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