Once the pinion angle is set, re-check the side to side measurements, and tack weld the perches on. Weld half of each side of each perch, and then go to the other perch so that you will not concentrate too much heat in one area at one time and warp the housing. Wet rags wrapped around the tubes helps. http://www.moparts.org/Tech/Archive/rearsusp/6.html