i think the only difference is the width of the belt. changing the belt would be the first choice. alternately, you could change the alt pulley or the alternator to get the wider pulley. if you go to the later alternator you may have to change out the long pivot bolt or get bushings for the ac delete bracket. the late alt uses an 8 mm bolt and the early uses 6mm. interestly, the 924s alt uses the wide pulley with the 8 mm pivot bolt.
you could get the bushings at mcmaster.com
i would think you should be able to get the belt from a local supplier though.