Thing is: Vought did not envision the F4U as a high-production machine on the order of 12k, hence the expanded wartime scheme with Goodyear and Brewster. Wish I could find my long-long ago notes from the interview with engineer Rex Beisel for the 1979 book. IIRC the center section was one of the most complex single-engine airframe components of the era, requiring some redesign to ramp up deliveries.