I forgot to take pictures of the inside
but, the center section is just held in place by the axles. Each axle has a spacer with a set screw and shim washers. This keeps the axles from moving in or out and also sets the backlash. The pinion is supported by 2 bearings and didn't require any shims. The truck deffinately turns better with an open diff but I think it will get stuck a lot easier now much like the real truck does! I drove it around with a cinder block in the back and it seemed to work fine so hopefully this holds up.
Thanks for the comments!