From what I've researched so far (looking into all this myself)
285/70 on stock rims will rub even if you have got the spidertrax spacers. I dont think it will be drivable without the spacers.. your tire will probably not clear the UCA
to run the 285/70 u need the spacers for sure, and also have to do some trimming on the bumper/body mount to run that tire without any rubbing.
If I'm misinformed, I apologize, but I just started researching all this myself.