Why not just wire it the way it was intended, with a kickdown switch? It's necessary to kill the ignition momentarily to allow the solenoid to retract the lock pawl properly and engage direct drive. The kickdown does that by shorting out the circuit from the coil to the distributor for a fraction of a second while the spring-loaded solenoid plunger retracts. A simple toggle switch engagement/disengagement does not do that, and could result in damage to the overdrive unless the driver disengages the clutch while shifting out of overdrive with the toggle switch.
Jerry

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