I assume you are talking about fly wheel horsepower. 225 is the stock fly wheel horsepower output. In reality, our stangs are around 190 REAR wheel horsepower stock. You don't really have anything you in your mod list that would up the power to any significant level. So, you are pretty much as the stock ratings.
Yep, always flywheel. It's easier for the company to test the actual engine output because they build the engine before its in the car. In order to give RWHP they would have to dyno the car. In either case, the fly wheel horsepower is always larger because it doesn't contain the lost of power that is consumed turning the drivetrain components. Putting the fly wheel horepower ratings out sells cars much easier too.