My '38 vents had a clip on one side and a screw on the other. Heaters and defrosters were a dealer installed option. Even though my '38 never had a heater/defroster until I put one in the holes were there. Maybe someone has altered yours sometime in the past???? Even if that's so you can still drill the holes. Maybe someone has a good pic showing that area sans vents that they'd like to share?

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Name your dog Naked so you can walk Naked in the park.