99 runner need tire size help

[rvg112]

i have a 99 limited with 3inch toytech lift. i want to run larger tires than 285/75/16 .. i would like to run 315/75/16 i plan on gettin 1.5inch wheel spacers and possibly cragar soft 8s with a 4.5backspace... will that fit? if not what do i need to do so these will fit? thanks all...