"cubic inches can be converted to cubic feet by dividing by 1728". They can, but it's not accurate for a 4-stroke engine.
It's 3,456 because each cycle requires 720 degrees. Divide your calculated CFM by 2.
AFAIK the best design for an L6 street car has been collecting the 1-2-3 and 4-5-6 separately, into dual exhaust, no crossover, for about 100 years.
