price to narrow a B body 8 1/4 rear

I don't think that is cost efficient. The axles are C clip axles so you would have to find or buy the correct length axles or have axles made and use a C clip eliminator kit. Do they even make them for an 8 1/4? I don't know. Narrowing the housing isn't the big deal, it's the axles and stuff to go with it. And then you still have an 8 1/4 rear that isn't all that strong.

Now if you could find an 8 1/4 A body rear then that wouldn't be too bad if the price was right.