Really looks like the first image is a later version of the second image with a chunk cut away. If not, and you want to add the bulge and the rib to the part then my reply would be "I would not start from here".
Seriously without know the design intent and constraints, and how the part has been build so far, really difficult to give advice.
would be a lot easier if the original feature model was available. Would then be a matter of editing and deleting features.
Otherwise you are going to have to build the bulge surface from curves, extend the rib a little then create curves to sweep the rib round the bulge.
Had another look at the part, there is quite a easy way of doing this.
The part is complicated by the blend that have been cut away. Looked at direct modeling but a few issues with that. However the main design is actually just regular surface.
Extract the cylindrical, conical and planar faces.
Trim and extend them against each other.
Build the top surface with fill or N-side.
Bridge curves to define the missing part of the rib
Then reconstruct the blends.