Here is a tip. To give you a ballpark number for the right sized carburetor, simply double your cubic inches, and that number should be reasonably close for an average performance build. 383 X 2 = 766 so a 750 would put you in the ball park. One step smaller for a mild build and one step larger for an more radical build. There are always other elements that play into choice, but this method works well for getting you close. An old mechanic told me that when I was a teenage gear head, and I have always remembered it.