Craig,
Its a clean bolt on but you need the manifold from an '05+ that comes with a VForce OEM as the RAD valve had an integrated manifold. Back in '03 I had to make my own manifold. Also, there is a close fit from the outer reed petals to the cases. The case area is a rough sand casting and should be cleaned up with a fine file, scotchbrite,and polish. The surface will actually function a a reed stop so you need it to be smooth or reed life will be crap.
Overall a worthwhile mod, I thought my '03 ran a lot better with it than the RAD valve. If your looking for big low end gains try and find the VForce II and run it in the "low tension" position.