Agreed on the Ford assembly plant installed sway bars, every decent original that I've soaked in evaporust comes out a medium to dark shade of natural metal. Similar to coil springs. For '65 GT350, the ones installed at SA - I am seeing possibly both unpainted and painted sway bars. Tried to attach pics, but 'folder is full', so will try again later.
First pic I have is possibly of an early '65 GT350, maybe a prototype. It is an undercar photo showing the front suspension. The sway bar looks lighter color than what I've seen on Ford assembly plant sway bars. It may be an earlier unpainted version?
Second pic I have is a high resolution of the pit area at LAX with a big pile of sway bars. Zooming in on the pic, the bars are all at different angles and have a sheen on them that looks like paint.
So, for SA installed 1" sway bars, those may have been natural or black.
As far as finish, as mentioned, soaking in evaporust does a great job of preserving the finish while removing all surface rust. I have simply coated bars after soaking with protective coating like Boeshileld or RPM product that ECS sells. I've tried insta-blak with mixed results. Gun bluing is hard to get a consistent look.