Where is it written one must ALSO move the front hangers in?
I believe in many cases the springs are angled in at the front. There are minor advantages to that angle being angled in. Most cars have tire clearance issues behind the axle, and offset rear shackles address that quickly, but the spring perches still must be relocated in any case. The rear offset shackle distortion mentioned is IMO without basis in any street driven car.
Try to do the job without the front and rear offset hangers on an A Body. Max offset on the MP A Body shackle set is 1/2 " even though they call it a 3/4". Anything over 1/2" and the front hanger is up against the frame rail.