Putting a 1/2" side load on the springs is dumb. And because the perches are 44" c-c on the B body rear and 43" c-c on the A body rear you're also losing spring clearance for the tires. In addition to all the side load on the springs/bushings/hangers.
And Barracudas, Dusters and Demons have an extra 1" of width in the outer wheelhouse, which is what makes the wider rear axle easier to deal with. The higher wheel opening helps as well, but the extra inch is a big deal.