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

By the way if you don't have a factory shop manual, run over to MyMopar.com and download one for free. Some of the guys here, got it there.

Here's a link to the limiter plate kit if you are interested.

https://4secondsflat.com/Mopar Mechanical timing limiter plate.htm