I thought it was an A body rear end?

The width spacings you posted match up to a 71 - 74 B Body, but with the perches on top of the tubes, it probably came from a truck or van. What type of rear end is it - 8 1/4, 8 3/4?? The A Body spacing for an 8 3/4 is 51.8" and 43" perch to perch. If the purchase price was right, and it's exactly the rearend you want for your A Body, you could always get it narrowed, but it would be probably cheaper to find another A Body unit. Hope this helps.