This is why I asked for input back when. When I add the shim the rear pinion will have a 4.5 angle and the trans will have a 5 angle which will give me a .5 degree delta between the front and rear spider angle, which is what I am shooting for. If the angles were opposite then they would be additive but judging by the lack of response to my OP, I am guessing this is something that few folks have thought about. As of now I haven't done anything but I am just following the instructions in the GearVendors shop manual at this point.