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