"I have March pulleys....wonder if they offer a single alternator pulley by itself?" - blykins
Well,it is a good news/bad news type of deal.
You can buy individual pullys from March.But in all their many different sets the alternator pulley size remains the same.
2 11/16" dia..
Yesterday I ordered a 5 1/4" water pump pulley to replaced my 6 1/4" directly from March.
Performance pulley to high water flow pulley.
The crank pulley in the two sets are the same too, 5 1/2".
http://www.marchperf.com/pg33.html