well actually SS the A-990 cars or 2% cars did exactly that... they took an A body spring (20" front segment) and put it on the b body cars (22" front segment)
but for what were doing i agree not much difference
That's right, they did. BUT, they also used the 2" longer front hanger to get the rear shackle mount angle right. that's why Mopar performance stills them and if you read the foot notes in the SS spring section, you'll see that the longer hangers are required on B bodies....and they are also needed on some A bodies as well.