Need Help! With solid/surface generation!

I can't figure out the correct way to generate this surface/solid I need to complete my part (motorcycle clutch cover). Help would be much appreciated! You will notice I have a solid for the sides and a solid for the bottom, I now need to have create the joining solid/surface to make it a complete part.

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Clik here to view.Image may be NSFW.
Clik here to view.Image may be NSFW.
Clik here to view.

Image may be NSFW.
Clik here to view.