Theres no such thing as a Ph1 172 Cup. But as you're in Australia it could be what we call something else here.
But if its the Mk2 172 Cup, then all the parts are the same as the normal 172.
The proper cup (ie 172 cup) gearbox has a hole in it to put a speedo drive in whereas the others don't.would the gearbox `s be all that different?