Help Identifying a tub overflow cover for old brass connection

[tadye]

I'm hoping someone can help me with the name/type of overflow drain connection in the picture. This is in a drop-in tub and the connection and overflow drain pipe appear to be brass. The house was built in the late 50's and we're missing the overflow plate. The connector has 4 screws and is the same depth as standard overflow cover plate. I think I could rig a standard plate to that would still allow for water to enter, or replace it all together, but would like to know that the intended plate looks. Any information is much appreciated!