I've only done one of these, and it was a long time ago. When I did mine, the extension piece was separate, as was the original I was emulating. I shaped it around a piece of pipe that was close to the same curvature as the forend minus the thickness of the metal, before inletting it. That way, there was very little brass to file off once the inlay was flush with the wood. I hope that answers your question, Chris.