Bathtub overflow rusted away

In a house built about the 40's, the bathtub has an overflow plate with a center screw. The screw goes into a bar that runs across hole, but it's rusted completely away.

I was wondering how this can be repair? I think the drain tube is still intact, but the gasket is not. Most of the plates I see have two screws, but there's nothing to screw the plate to. Is there a kit that we can purchase to fix this?

Thanks.

Paul

How about a picture. Most of the metal plates with a center screw were attached to the overflow fitting with two bolts which were in the correct location for a two hole overflow plate.