Super Six fuel mileage

I have a bone stock '79 Super Six engine in my '64 convertible, and since the rebuild, I've only had one opportunity to check it, so the numbers don't mean much. The engine isn't broken in yet, and in this 100 degree weather, a carb full of ethanol fuel will evaporate in two days.

Most of my driving is in town or rural two-lane, and the first tankful was about 18mpg. The improvement is 2mpg over the tired '64 engine with the same Super Six setup.