Well..seeing as the alternator tightens the belt on a swivel, you can probably use the same alternator belt. but you may need a shorter PS belt ( and maybe AC too). Put on the pulleys, and put on your old v-belts, and see if theyre too short or too long. Any auto part store will help you match up bigger and smaller belts. It's a pain in the butt, but its the only way.
( i have the march pulleys too, look great!)