If you are just wanting to square the rearend in the car. Find the center of the front crossmember and drop a plumb bob from the center to the floor. Drop a plumb bob off each end of the rearend to the floor and measure in a triangle. You can use one plumb bob just put a dot on the floor with a sharpie. Take a file or cutoff wheel and cut notches for the string to lay in for future reference. Make sure to remember your measurements so you can alway's go back to it.