Sperry had developed a gyroscopic autopilot system around the time of WWI and successfully demonstrated it on several occasions during the interest period.
If Japanese philosophy at the time considered a steel plate behind the pilot, or a radio to be excessive additional weight, then I suspect that the addition of the gyro autopilot, with its extra instruments and hydraulic or pneumatic flight control actuators would be an absolute non-starter. Especially considering that the autopilot didn't contribute anything that a well disciplined pilot couldn't do himself already
In addition to fuel starvation and fatigue, it must challenge your navigation skills. It's November 1943, and four A6Ms from Taiwan are sent to reinforce the garrison in Guam, departing for Orote field, located 1,700 miles away. At a cruising speed of 200 mph it's at least nine hours flying, meaning that a portion of the flight may be at night.
The flight looks simple enough, set your compass for SE and off you go. But the winds will push you around, its nothing but wide open sea, and it's also typhoon season, meaning visibility may be limited. And with a max ferry range of 1,900 miles, our IJN pilots do not have a ton of endurance for course deviations. I'd want a G3M Betty or similar with a dedicated navigator onboard to guide the way.