As long as the transmission housing is the same from year to year (which it is) and if the tranny from the two different years are pull-type clutches (which they are), you'll be fine.
btw http://cgi.ebay.com/ebaymotors/EXED...hZ019QQitemZ8076504366QQrdZ1QQsspagenameZWDVW and http://www.clutchcityonline.com/subaru_wrx.htm