Swapping rear end question.

HemiSSDart said
The only B-Body rear that is almost a swap for an A-Body is a 65-67 unit and the spring perches are only 1/2" wider than and A-Body. I have done this swap a couple of times, it is pretty much a bolt in and the rear hangars can make up for the 1/2" difference. The biggest issue on a Dart is that the wheels will have to be made or found for the correct backspacing to bring the tire in closer to the frame rails, I had a set made. On a 65-69 Barracuda and a Duster/Demom it is much easier to find wheels as they wheel wells do not shroud the tire nearly as much as a Dart...

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.