what all do i need for a 1998 jeep cherokee sport spacer lift?

[janis]

i have a 1998 jeep cherokee sport and i want to higher it a little so i can fit 31" tires, but i dont want to buy a suspension lift i was just wondering what all will i need to lift my jeep 3" with spacers, i thought i found them on ebay but then i read something like i need back blocks to or something like that because spacers are only for the front????