I have one in my Valiant, but I am using 97 Mustang wheels. I measured mine out at 59.5" wide, same as the early B-Body that seems to be the best swap for an A-Body. BTW, that put's it at less than 2.5" wider overall, little less than 1.25" wider per side.
If you have 1.25" that your wheels could move out, you're good to go to swap it in.
You will need to remove the old perches, and weld new ones on at 43" center to center. If you do them one at a time you can do it without having to mess with finding the pinion angle, too.
I say go for it. People have been putting early B-Body 8.75" axles in A-Bodies for years without deep offset wheels, I think it corrects a factory flaw anyways.