You can keep the same wheels, and yes you can only put drag radials on the rear if you find ones that fit. It is called a staggered setup.
I got 9" wide wheels on the front and the back of my car, but, on the front I have 255/35/20's with the 255 meaning the tires width. 35 the primarily the sidewall height, and 20 is the rim size. - On the rear I am running a 275/35/20 tire.
Same rims all around, just different tire sizes. Thus meaning you can never rotate them.
Like I said, if you can find a drag radial that is like a 275/40/19(going off top of my head for these numbers) or something similar, that would work for the rear.
For a 8.5" wide rim, you wont want to go any wider than a 275, maaaaaybe a 285 tire.