reusing antique overflow coverplate with new drain?

Just wanted any suggestions. We just got our 80 year old drop in cast iron tub refinished and wanted to use the old brass coverplate for the overflow hole. It has a single center screw hole and we are trying to find a replacement waste overflow system that will work with it? Any suggestions as to one that may work. Pretty standard sizing and will be unexposed. Thanks.

It'd probably be easier to just drill two more holes in the brass coverplate, so you can get a good seal. Then just glue in a "dummy" screw for the middle hole.

They make single hole overflows for tubs just keep looking at the big box stores and any local plumbing supply.