Originally posted by Vinyard
Overdrive has to do with gearing and not one-way. A front diff will also allow you to have an overdrive.. 
Read slowly and you'll understand
A front one way will allow you to run overdrive efficiently. You can run front overdrive with a car equipped with a front diff.
However, there are some drawbacks when doing that. That is what I explained in my previous post that front overdrive with a front diff will not work as effective as a front overdrive with a one way front.