Hello and thanks for your reply. I have no idea what postcript / PCL6 drivers are, but from the research I have done they seem to be alternatives to CUPS drivers? I will try to find them and report whether they worked for this printer.
Thanks for the pkg trick. I am a bit concerned about causing a kernel panic by forcing the original driver and modifying the installer. Before trying that, I want to try the option below.
What I have actually found are the ppd files. They were inside of HP's driver pkg, buried deep. I have extracted the one for macOS 10.6: HP Photosmart C4600 series.ppd. The question is, how is this loaded into CUPS? I believe it might be a matter of:
1 Copying the file to /Library/Printers/PPDs/Contents/Resources/en.lproj
2 Connecting the printer and following the wizard
3 When asked about the driver, locate it on the path above and select it.
I am unsure if this will work given that the ppd was designed for 10.6 and I have 14.4.1. I will have access to the printer tomorrow. If this works I'll make sure to draft a step by step guide here.
If you know a better / easier way to load the driver into cups, or think this might fail, please let me know. I'm not super techie.
Thank you