I drove my 63 Nova for ten years as my daily driver and tracked mileage with every tankful. I ran water heat to the manifold. I drove the car with the primaries oriented like a V-8, then changed to the primaries parallel to the crank and towards the outside of the engine. I had to increase my jet sizes, but my mileage still increased and drivability also improved. I suspect that having the primaries as far from the engine as possible increased fuel distribution to the end cylinders at lower engine speeds. When the engine was spinning fast enough to open the secondaries, the air was moving fast enough through the manifold it didn't matter as much.
