im guessing your going to be riding in the forest or somewhere that a spark arrestor is required?
dont quote me on this, but i believe the design of the muffler works as a spark arrestor. the exit for the exhaust kicks out the bottom of the muffler right? this basically is the arrestor part, because if a flame ignites in you exhaust pipe, it doesnt have a unrestricted exit out the exhaust.
at least in the pacific northwest, the main method used for checking exhaust by the forest service is shoving a stick into the exhaust. if the stick cant go all the way through your muffler into the mid-pipe, your golden.
will still want to check with whoever the authorities of the area you plan to ride with, and if it still might be an issue, you can wrap some fine mesh wire around the exhaust exit, that should also suffice.