How should my duster handle

Make the car steer like a modern car. Add low profile tires like modern car. Add a super stereo system like a modern car. Put in modern seats and dash. Swap out the engine and trans for a modern car's. After a while....this is your 1970 Duster:

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Add better steering, tires, suspension and a modern motor and trans and you are closer to the below than a new Dart:

Dodge-Challenger.jpg

Maybe you don't like those either, and that ok. But it's still a better representation of what an updated A-Body is.