Measure and then re-measure to ensure your rear end is PERFECTLY centered in the rear wheel opening, or I'm not sure that you will be able to fit a 30x9. If you do have room for a 30x9, it will need to be a radial slick. A bias slick will grow.
I had one Hoosier 30x9 radial mounted on my spare Weld wheel. It fit on one side, but not the other. When we replaced the rear end, we had to move the center pin locating hole to square up the rear in my car.
I now have the 29x9 bias Hoosier on mine with a 15x8 wheel with 4.75 backspace (.25 spacer).
Clark