as Squire said, if you are going to put the rear end back, it is best do it before driveline is done. That said, I have done an axle flop and not changed driveline on different vehicles. Drawing it out on paper, you can use geometry to easily figure out the difference in length after you move it, I would assume it would be 1/2" or less. (probably more like 1/4" difference).
