I'm the new owner of a 1956 Southern California home and discovered this curious plate on the stucco exterior above, and to the left of the front door. There is a sconce mounted above the same door.

Removing it revealed that there are wires inside, which makes me think that it's a junction box (just a guess - I'm not sure of its purpose). Regardless, I think it should have a weatherproof cover (the hole in this one is concerning) that can easily be removed & replaced in the event that electricians ever need access (this one was siliconed around the edges to seal it)

The box is round has 2 screw holes, presumably for attaching a cover, that are approximately 2-3/4" spacing. I searched for round junction box covers and they all seem to be 4" diameter these days. What's the proper way to cover this?