The old chart plotter on my 2004 era sailboat is portrait and most new chart plotters are landscape. Making holes bigger is self explanatory, but the existing hole is 1” too tall for the new one (Garmin GPSMap 943xsv is what I am thinking of). The rest of the surface area is covered in other equipment which makes this more difficult.

Got any suggestions on how to handle this issue?

I had thought of potentially getting some starboard and making a whole new surface that has a new layout. Sealing that properly seems difficult, but not impossible. I would welcome any suggestions there as well.

The good news is that the old Raymarine seatalk 1 (not NG) has already had converters installed to establish a NEMA 2k backbone to power the autopilot. So that is one less thing to worry about. I would also be replacing the radar since the old one won’t be compatible with anything modern.