It will just be a 4 pin straight header. You could put either or on the header, but it’s mainly used for the plug and play USB equiptment that you buy for about $30 if you want to DIY datalog. Most all tuners are going to have the usb interface. The serial cable hookup was the old school way of doing it really. Many laptops don’t even have a serial port on them anymore.
If you request the DB9 port to be added instead, I could do that no problem, but it’s going to cost you a little more as I’d need to add the connector and mount it nicely in the case.