John Rumm wrote:

serial comms software on the old machine (like Telix / QuickLink2), and
something that can run ZModem on the modern one (Like PuTTY, with the
ExtraPutty add on that gives it Zmodem compatibility). The just upload
files from one, and download on the other.

I can't remember if procomm/telix/etc can do a recursive copy of a whole
drive in one go, but kermit can ..