This is the shaker entry duct for the various 73-81 Trans Am's .. the flexible duct connects to this at the clamp mark.
Length of oval hole is approx 140mm or 5.5 inch and the height of the oval 1.5" .
The ROUND hole is 90 mm or around 3.5 inches.
This is for the fresh air duct into the side of the air clearner housing.. that then couples to the flexible pipe to the LHS (US Drivers) around the radiator support panel.