As I mentioned in the previous step, we’ll be building this part with a short explanation, because you're familiarized with the tools.
1. Position the model as image below.
2. Create a plane object and position it as this image (convert to Editable Poly).
3. Now add these details.
4. The model.
5. Select the mode sub-object Polygon and extrude. Clone it as the image below.
Detach the two parts and don't forget to weld the vertexes (Shift + w).
6 .Delete the faces in the prominences.
7. Make sharper the red details...Move the vertexes.
