There's many that will work, some are more correct than others for numbers or year, all can be upgraded internally to suit current setup.
17058264 for regular 400 Auto, 17058263 for W72 Manual, 17058266 for W72 Auto are the original 1978 numbers. There's other carbs to suit late 70's Pontiac engines that will also suit and can be rebuilt to suit. While they likely cost more, the correct carb will also be worth more with the car, and simply work as it should, and everything fit where and how it should. Did you have a carb on it now?