I have the Corinthian series from about 15(?) years ago, and I need to replace one. I can't find anyone online who sells them. Did you go ahead with the install? Where did you get the instruments?
I replaced my DMI ( 1981 vintage) with ST60 raymarine flush mounts. The flushmount kits require a square cutout accomplished with a router and template. The cutouts are just a little larger than the DMI holes. Needed a Raymarine masthead unit, but was able to make an adapter PCB to interface the DMI speed transducer to the ST60 Speed display. Now I have VMG and a race count down timer and the displays also appear in a window on the chart plotter at the nav station.
The circuit board converts the signal from the DMI speed transducer to the raymarine required input level. It allowed me to change over to Raymarine ST60 instruments without having to haul the boat to change out the speed transucer through hull puck. I loose the water temp function from the raymarine transducer, but being in a lake, I have a lack of gulf stream to be concerned about. The wind sensor is the stock ST60 masthead mounting block with cable run inside the mast. I left the DMI mast head sensor up and can re-install the DMI instruments if I ever need to.