With 31's on a 2" BB you will rip off the fender flares if you go offroad. Extend you bumpstops 1" and you should be fine.
Extended bumpstops prevent your tires from contacting the body and causing body damage and getting the treads cut on sharp sheetmetal. They also prevent damage to your shocks and springs. You will destroy your shocks if you slam them down until they are fully compressed. Your leaf springs will flex until they get inverted and then they will begin to lose their arch.
Hockey pucks are a cheap way to extend the front bumpstops and there are longer XJ factory bumpstops and/or you can add spacers to the rear.
Go here and read - http://members.aol.com/Stvns/XJhelp2.html