At 70ish years old, it is hard to say if what is currently installed is actually original. Someone might have changed the wheels 20 years after it was built and they would have been installed for 50 years by now.
That said, the GM Information Kit says that the original wheel should have been a 16x4.5.
I am not super clear what you are asking, so if this doesn't help maybe you can clarify your question?
