
He also helped me out on the correct USB-to-serial adapter (cheap on Amz). My existing one clearly did not support full hardware handshaking as when I plugged this one in, I was able to transfer a file from my Windows 10 laptop using the Eazylink2 software, first time.
(I tried on Mac and Linux first, but in both cases the EZL2 client failed to start up, throwing cryptic errors - I will let the devs know. I suspect booth my macOS and Linux installations are simply too new, whereas Windows seems quite happy to run software from the neolithic)