What would I gain from a 4bbl on a 273?

My '65 Barracuda has the Edelbrock 1406 4bbl 600cfm and I'm quite happy with it. The guy who worked on the car for the last owner said that it now gets about 253 HP. He had tried 2 other 4bbls on it, and a 2bbl, and this one worked the best. I recently put a Pertronix igniter on it , too . I'm not sure if that has increased the horsepower past the 253. It is getting better gas mileage though.