We put a 15% pulley on this weekend and changed the belt. Autozone has the wrong standard belt size listed in their system for the 2003 MCS. It looks like it is the size for the standard MC. They double checked the number several times and it came up the same each time for that year. We had them look up '02 & '04 and they were correct.

I ended up purchasing a Goodyear Gatorback that fit the new pulley perfectly. The item number is 4060537 6PK1365.