Maybe there is some confusion here. Most of the long runner set ups are a reaction, a fix for the loss of low speed power that comes with a new bigger carb. Then, the new longer runner, which actually helps the bottom of the power band, still gets blamed for the loss of low end that was caused by the big carb in the first place.
For illustration, put a longer runner (within reason) on a stock carb'd engine and the low speed power curve likely will improve but that long pipe will choke the engine at higher speeds.
Another way to say it - if you retain a short runner and change to a big carb, then between strokes the velocity/volume/mass in the port falls off too quickly, between strokes/valve events, as compared to a smaller carb. If, however, you add a longer runner to that big carb, then more volume/mass of air is transported over a longer time and that pushes the average velocity/volume/mass higher between strokes/valve events.
So . . . . within reason, with larger carbs, longer ports broaden the power band, help retain the low end.
Tell me if I'm wrong.
Another question though - where is it best, within that 14" port to place the carb? Close to or far from the head? According to inside diameter of the carb, is there a ratio that predicts the ideal length for a velocity stack?