The full bulged canopy was standard after the 689th Corsair was built. Some AC before #689 had the one panel above the pilots head bulged for more headroom. The recessed turtledeck area ala the P40 was standard on all production models. The late model F4U1s had most of the modifications, canopy, cowl flaps, raised seat, raised tail wheel, new tailhook, longer stroke landing gear oleos, etc.