CUPS 3.0 is a major architecture overhaul with moving away from PPD files and just relying on IPP Everywhere, splitting local printing from network printing support, and various other design improvements.
I'm glad it helped. I keep meaning to try it on my wife's Mac at her exercise studio, as the Mac says it has no driver for her 12 or so year old HP printer.
Apple started using cups in 2002. Apple acquired cups Feb 2007.Apple bought CUPs in 2002 so if you're wife's Mac is not a relic, it should be fairly easy. The other unknown is the Printer Language used by the 12 year old HP printer.
If
Postscript - you should be good to go for basic printing
If
PCLx -> Installing ghostscript on MacOS
If ZjStream wire protocol -> Installing HP Color Laserjet drivers - Apple
On my Brother HL-5450 a firmware update enabled the universal print everywhere driver but at the expense of some printing capabilities. I ended up reverting firmware.
If you place the *ppd in /.... If anyone has any ideas about better ways to get the required .ppd I like to hear them.