Originally Posted by S10xGN
Could only be the tubing, shaft ends, and labor. As for measuring, I've always put the car up where I can get under it comfortably (making sure the rear axle is fully loaded) then measure center to center on the u-joints with the trans yoke pulled out 3/4" from fully inserted. There are other ways to measure, so whatever you use, be sure to tell the shop exactly how you measured.
Now when you say rear axle fully loaded do you mean like jack it up in the air and put jack stands under the rear end and place the car weight on it, or just while the vehicle is sitting on the rearend normally.