Re:
Bikepedia indicates you have a 1998 Rift Zone that has 4" travel, same as my 2001 Shore Line Trail. You need a 7.25" rear shock, in new money 185mm (which in my experience is a 184.1mm Fox).
Of course I have already been branded incompetent by some posters here, so the caveat is go home and measure. Of course we both know what you need and it is not what the majority are advising!