After a bit of fitting, standing back and looking, and more fitting, I've decided to use the headlight assembly below. I think it is an early CB160 housing, with a big oval speedometer. It also sports an old school headlight, with genuine "made in japan" Stanley glass lens.
I managed to gently pry away the thin retaining ring, and pull the entire assembly apart. The chrome plating on the inside of the reflector has flaked away, so I'll need to fix that. But the lens itself is in great shape, as is the chrome trim ring.
I've already deflaked the reflector, wired brushed off some rust, and dipped it in muriatic acid to eat away the rest of the rust. Then I'll either spray the reflector with some chrome paint, or lay down some aluminum foil. I'm thinking of "ambering" the lens too, using some amber colored stained glass paint that Krylon sells.