Yikes, that's a lot for something you'll have to modify. For reference, the spring perches on an A body are 43" center to center, and depending on what B body rear that actually is, you will have to move the perches in, or relocate your springs. 1 3/16" on each side is a lot, especially on an early A body! It's a tough fit for a Duster, an early A body is even narrower in the wheelhouse than any other A body! Much more research and measurements are needed if I were putting out $850 for something that wasn't bolt in ready!
There's also the bolt pattern difference to consider, just thought that needed to be mentioned!