well the fronts cant be moved left to right as the driveshafts determine how far in/out the wheel sits, only the camber/castor/toe can be changed so that makes no difference
i no the shells are not true by a long way to start
the question is......will i benefit/notice the advantage (if any) of the rear wheels being aligned with the fronts rather than aligning the axle to sit the rear wheels nicely in the arches?