B body rear axle in an A body

I think it would work depending on how big of a tire you use and the springs used in the rear.
For example, on my car with the Super Stock springs, I could probably run that wheel with a 275 60 15 because the springs lift it up more on the back end and the factory wheel tubs don't come into play.
If your car is lowered for handling or even stock ride height, the tires might rub with that size of tire.
You'll have to mock it up and measure before you buy tires is my advice.

Good choice using the offset hanger kit from Dr. Diff.
He is a great guy and his knowledge, prices, and shipping are very good.
I have bought a fair amount of parts off him in the last several years.

If you decide to change the gears in the 489, get the crush sleeve eliminator kit from Dr. Diff.
I did and it worked out very well.

I would like to run a 275 on a 15x8. I have the factory 8.25 in it now with a single leg 2.71? The car has the MP 3” relocation and it puts the leaf spring right next to the gas tank on the right side negating the use of tail pipes and factory tips in the stock location. I have a set of tips that I would like to use on it so the leaf springs have to move back out.