From what I have researched and been told by driveline shops: if you are running a DC at the t-case side of a rear driveline, the rear pinion should point at the t-case flange, or maybe 1-2 degrees down to allow for pinion to rotate up on acceleration. If you have a single jointed shaft, the t-case and pinion should be at the same angle. So if the t-case flange is down 6*, then the pinion should be the same. Basically the flange surfaces should be parallel if you were looking from a side view, make sense?
Again, this is what I've been told, not having experienced personally...
