[Asshat]

Can you post a pic of your dash and how the cable control looks? And, maybe the shifter too?

I'm not sure if this three-speed OD is worth the trouble. Seems like a T5 is more expensive, but a lot easier to implement and use.

There's a lot involved with this conversion:
3-speed shifter, modify trans cover.
cable control
solenoid wiring
kick-down switch/linkage

The driveshaft and trans mount is a given with either 3-speed OD or the T5 trans.




With the overdrive engaged (handle in), the transmission will freewheel below 20-32 mph (depending on the car's rearend gearing), which means the engine will drive the wheels, but when you lift off the throttle the wheels won't spin the engine-the car will coast as there is no engine braking. However, once the car is up to the required miles per hour, the governor closes the electrical circuit, then when the driver momentarily releases the throttle the solenoid locks the sun gear of the planetary set and the transmission shifts into overdrive (which also means there will be compression braking when you let off the gas). Shifting out of overdrive happens one of two ways: slowing down under the governor cut-in speed causes the solenoid to release. Or, if the throttle is floored the kick-down switch is activated. This does two things; it interrupts power to the solenoid and the ignition circuit momentarily. With power to the solenoid cut you would think it would release the sun gear and the transmission would revert to direct drive. But under load the solenoid pin is "trapped" and can't release, so shutting down the ignition system briefly (it's said to be one or two crankshaft revolutions) the load on the solenoid pin is released, it immediately withdraws releasing the sun gear (which means the transmission is in direct drive) and the ignition system is back on all in the blink of an eye.
Thanks to the governor, the transmission will go into overdrive once cut-in speed is achieved, so around town in traffic using overdrive in Second gear is a natural-it's like having an automatic to a certain extent as the transmission will shift back and forth between direct and overdrive as the speed dictates. On the highway, cruising in Third overdrive and stomping on the gas pedal will cause a downshift to direct for passing.
One other peculiarity of these overdrives should be noted. When left in overdrive mode, more than one parked car has been known to roll away. Most transmissions had an internal mechanism to lock out overdrive in reverse, which would keep this from happening, but the only other way to keep the car from rolling in any other gear was to disengage overdrive and make sure the parking brake was operational.