There are people building HD6309 SBC, which is great to hear! I've received a couple of questions regarding construction that I will address in a couple new project logs:

FT230XS Configuration

A "fresh" FT230XS device will enumerate as a VCP, but needs a tiny bit of tweaking in order to operate as intended on the SBC PCB:

The FT_PROG configuration tool is available from FTDI here.  On the same page is the FT_PROG user guide. Connect the USB, start FT_PROG, and use the "Scan & Parse" option to find the FT230XS device. Afterwards, the configuration can be edited:

In the USB Config Descriptor section, set the following.
    bmAttributes = Self Powered
    MaxPower =     500mA

In the Hardware Specific section, set the following:
    CBUS Signals
        C0 = VBUS_Sense
        C1 = TX&RXLED
        C2 = Drive_0
        C3 = Drive_0
    IO Pins
        CBUS Drive = 8mA