If you order one, it will only come with one so for a dual set up you will need to order two. As far as the outlet, the 4in cap is specific to the 4in exhaust can, so your going to want to make sure you order the correct cap for whatever your exhaust can diameter is. The outlets are going to be pretty much the same size.
If you're current end cap looks exactly like this, than this will mount. It must be a newer exhaust purchased within the last 2 years. If you have any questions regarding fitment, contact our Sales Team at 8888-676-8853