Using an HP laserjet 6p with my Imac (on 10.15.7)

Bit of a doozy - have an utterly bombproof HP Laserjet 6p - utterly reliable, prints thousands of pages in black white which is all i need.

obviously it uses LPT1 - been running it with a print server but that has given up the ghost with various kit changes. I now have a converter cable

Got a cable that allows LPT to USB. Downloaded the Gutenprint driver as well as the appropriate USBTB driver.

No dice.

Any clues?