Importing a Nissan Silvia-powered 1973 MK1 Ford Escort

There’s no reason why you couldn’t bring it in and get it registered for road use. To bring it in you need an import permit from the Department of Infrastructure and Transport in Canberra. That allows you to land the car, after you need to consult your state authorities to get it approved for registration. Rules vary from state to state, but it is most likely that you would need a report from an approved engineer.