If you can find an old Powerprint cable (USB to parallel) and software, you might be able to get this working in OS 9. You will have to check to see if there was software for this printer
The other way to do this is to get an external HP JetDirect network box so that you can put the 6L on an ethernet network. I don't know if OS X has the "drivers" to see this printer. You might need to try Gimp Print