Decades of heat and sun can cause a lot of the plastic interior pieces of your squarebody to become brittle and break. A very common part that breaks are the air vents. Holley Classic Trucks has exactly what you're looking for with their new air vent outlets.
Dashboard Air Vent
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Package Information
Orderable Status:YesQuantity:1Package UOM:Smallest Pack (Consumer Level)Weight Variance:0.000000000Stacking Factor:0Inner Quantity:0
Extended Information
Emission Code:4