Bought my first mopar 73’ Duster and the bottom of the air filter pan is black (right above the carb). Any tips on how the 4bbl should be adjusted

Thats a coolant recovery system. The should be coolant in it along with a 10231 radiator cap.

The recovery system picks up excessive coolant when the car get hot and returns it when it cools off. It keeps the rad full all the time and keeps the nasty off the street.