As long as it is incomplete, with no wings and unregistered, I can't see it being anything at all to do with CASA any more than
a Catalina fuselage converted into a houseboat is any of their business.
While I'd agree that the obvious first things for the police to charge him with are unregistered and uninsured vehicle, I wonder what they'd come up with next if he had gone to the trouble of getting an unregistered vehicle permit (a limited time permit which allows an unregistered vehicle to be moved about for the purposes of repair, preparation for registration and inspection)? After all, an unregistered permit assumes that the vehicle may be unroadworthy - that's why you're taking it places to get fixed and inspected!
I'm sure they have some catch-all offence which they can apply here, "conduct endangering life" or similar.