In the end this is how I finished my cover off:
Satin Finish, with polish marks showing
Clear coated
Porosity Still Visible where difficult to polish, and slightly to the polished surfaces.
Mine still had an area near the bolt which I believe to be a casting imperfection rather than road blast. There was no other consistent road blast on that surface so I left it after polishing. Notice similar features in the shouldered area for the oil ring groove.
Regards,
Steven