I remember hearing back in the day of people getting OS 8.5 - 9 to work on PPC upgraded Quadras by using a program such as Wish I Were to change the Getstalt ID to that of a similar Power Mac model. For example, if you're installing onto a PPC upgraded 610, you'd change the ID to that of a 6100, if you're installing onto a 650, you'd change the ID to that of a 7100, etc. Not sure how well it works, and even if you did get it to work, it'd be incredibly slow, but anyway its just an idea.