Here is how I did a DD setup. This is the easiest IMO.
Made brackets out of 1/4 inch aluminum for the center diff.
Drilled two holes for the front bracket and bolted the rear in using the tranny holes.
I used the stock front drive shaft and an axle shaft for the rear.
Slap on battery holders of choice.
And you have a kick ass E-Revo.
Build thread
here if your interested.