i got a dual alt pully from rx7 club and was wondering what belts i need to run to get it to work

 

It depends on the diameter of the pulley. If it's an underdrive pulley, like most of them are, you'll need longer belts. Hit up a parts store and test fit different lengths until one works. If the pulley is close to stock diameter, you can get away with using 2 belts of stock length.