I did the same with a G4 Mac Mini. One suggestion for your hobby/business-- I went with a PATA->m.2 SATA adapter instead of PATA->mSATA. It works like a charm and when I built mine a couple years ago it was actually much cheaper. Obviously it completely saturates the PATA interface.
I ran 10.4 and Void (no longer maintained) so if there's a technical reason to stay on mSATA for Mac OS 9 please ignore. ;)