usually you should measure from the center of the hub to the flare so as to not being in the variation in tire sizes.
235s should be fine. 30x9.5s might even work. you can also keep the super awesome turbines you've got and add just wheel spacers
keep in mind that a lot of locations have laws against tires sticking out.
also, also, you can add wheel spacers to only the rear to make everything look balanced. see, the MJ has a bit of a wide butt... couple inches wider than an XJ back there. And so adding spacers to just the rear axle will bring those tires out and stop it from looking tucked-in.