I always run the non-Oxygenated fuel and add a lead substitute. This is important since it's a flathead and the lead cooled the valves. Without it, the valves could burn after a while - thousands of miles perhaps. It is possible the car had hardened valves and valve seats but if you don't know, it's best to add the lead. The problem I've noticed with ethanol, and I've had to use it in certain situations such as driving the car to meets, and the difference I've noticed is the car runs a little hotter and the mileage goes down a bit. A Corsair would have a four cylinder in it (Corsair Deluxe has the six) and I'm not sure if there was bulletin on the four but there was a service bulletin which recommends advancing the timing 3 - 5 degrees for better performance with the six. I've noticed if I do this, the ethanol causes the engine to ping so badly the car is undriveable so I have to keep it TDC as the original specs called for.
