Steve - might it be that floor is perhaps remade, from the fixings we can see? As per the comment about David's CHA list above, your car being "Australian" still suggests that it left Britain as a car (and perhaps has or had an EX mark painted on the rear crossmember of the chassis) because it has an Austin car number. What was it when new?, as we may be able to work out whether that other stamped figure WAS the body number from other numerals in the range.
Sadly AD Vans have no recording of the stamped body number on the Register - a heads up for owners to get on with it! So that doesn't help you. But what you hve recourse to is just ordering the heritage certificate from Gaydon with all your specification from new, because yours is an A9 car. Or you can just check the model/car type for 6 quid - a complete bargain.
You can also go and inspect yourself for free if you make an appointment. Of course, you won't find a body number recorded but you may find whether the body was changed, for instance.
Sadly AD Vans have no recording of the stamped body number on the Register - a heads up for owners to get on with it! So that doesn't help you. But what you hve recourse to is just ordering the heritage certificate from Gaydon with all your specification from new, because yours is an A9 car. Or you can just check the model/car type for 6 quid - a complete bargain.
You can also go and inspect yourself for free if you make an appointment. Of course, you won't find a body number recorded but you may find whether the body was changed, for instance.