Seth,
You only need two measurements, the transmission outlet and the differential pinion and they need to be very close to equal but opposite - tranny sloping down toward the back, and differential pinion sloping up toward the tranny. Basically, if you project a line through the transmission main shaft towards the back, and a second line through the differential inlet yoke towards the front those two lines will be parallel. Ideally the two angles will be less than about 3 degrees.