Can someone tell me or tell me where to find the specs for the rear D/A diff, backlash, pinion bearing preload etc.

I would *guess* backlash to be around .005" - .008" and Pinion Bearing Preload (TTR) to be around 15 - 25 #/IN. Obviously the Pinion Preload must be achieved and within the Pinon Nut Torque window. Those specs are pretty standard for most beam axles.