[supereal]

I have an overdrive in my '47 convertible. It is a 30% reduction when engaged. The car has a 3:78 rear, and if you choose a unit with that ration, it should do fine with the 4:11. It will allow you to leave it in overdrive a lower speeds. My Ryan unit mounts directly to the rear axle banjo, and I shift it with a cable sold for truck power takeoff application with the knob under the lower edge of the dashboard. I can run at highway speeds above 60 mph. Just be sure that your brakes and steering are in top shape for such high speeds.