Trying out a spreadbore carb on the Duster.

Like Mike said, if you want to try a spreadbore, go to a thermoquad. Tuned properly, they are awesome! Second only to the TQ is the square bore Edelbrock AVS2 series. The annular boosters provide vastly improved low and mid range throttle response over any Holley I've ever used. Edit: the AFB you got likely will run better if you also get a calibration kit so you can tune it. Very few carbs are perfect right out of the box, and especially those that are rebuilt. You never know what parts the rebuilders put back into them!