Correct, no factory availability. The PPC Upgrade Kit for the 68k Duos did not include a TrackPad uppercase downgrade top. I've never seen one actually "ripped out' and replaced, that was just a bit of hyperbole.

But I have seen some variant or other of the 190/5300 with a rudimentary Duo TrackBall upgrade! }

Back in the day, the Duo 2300c was still a bit too expensive to do much hacking, so I did a couple of interesting 5300 hacks somewhere between '01 & '03. I never finished the Trackball Hack because I didn't bother to find the Analog Battery Tester I'd wanted to install in the left palmrest behind the clear window along with the TrackBall.

One of them was a CD hacked into a 5300. )