Jerry, that's one strange trivet. Is the patent date 1888? Not too clear to see. It may have gone in some kind of safety kettle but I don't know whos. The broiler may be complete as many or most broilers of that type were of the single broiler style with no cover or top piece. If it were a double broiler I would think you would see a tab or some protrusion where the two parts fit together or keyed together.
Steve