8 3/4, what’s it worth?

I would consider leaving the niner the way it is, and getting wheels with more backspace. Of course, I don't know what your situation is. That idea may not work for what you want to do.....
I have 2 sets of wheels and tires for the Duster, one with drag radials (295x50R15) and the other with slicks (29x10.50). They are 15x10 and 5" backspace for the DR's and 5.5" backspace for the slicks and fit fine (tucked with no poke). I just want them tucked in more now that I have mini tubbed the car.

The Dart has the standard width 8 3/4 and 15x8 ralleys that have 5.5" back space and 275x60r15's that are also tucked. If I ran the 9" out of the Duster (2" narrowed), I could go to a 4.5" backspace ralley wheel which looks way better in my opinion. If I went to a 2" narrower axle on the Duster, I could really stuff the wheels and tires I already have....or I could just leave everything alone and just run it.... lol