Welcome aboard!  I think your son is going to love the rig.  The other guys are right, it won't take much to fit 31's.  I could fit them now with no problems, I just can't afford them. 

Like where-abouts in central MN?   Any idea how far the drive would be for me?   Ive driven almost 2 hours to go mudding for 2 hours before.   And what time would you be going?

Like, right in the middle...   If you look at a map, find Brainerd and go north...  It'd be a haul for you I think though.  We'd be leaving my place in brainerd around 10 am...