I am replacing both belts on my car and need to know which I should be using..I have seen some people you slightly smaller belts for the SC...I will be installing a 2.2" pulley soon so keep that in mind.

what part numbers do I need to buy and what is a good vendor for gatorback belts?

autozone carries gatorback... sorry i dont know the part numbers though

they will have the stock ones for you.. then just get the next size down

Buy the stock sized belts and use a 3.5" idler instead of a smaller belt if you're going all the way to a 2.2" pulley. You need this for proper belt wrap.