The pulleys are "somewhat" interchangeable. It depends on the offset. A spacer can assist the offset.
The stock pulley is 8 rib. The stock pulley size is a 3.75"
The stock belt is a gates or equivalent: K080485 -GATES.
The Gates belt sizes are here: http://www.gates.com/oreilly/PDFs/SizeListings.pdf
Hope this helps!