Hey Welcome to the CRG!
As William stated, Vin and body number is the best place to start. There are many other clues that when combined may lead to other deductions. If your car was shipped to Canada it may be possible to find out how it left the factory.
If you want some open help from members, Post some pics of your body tag, and some pics of the car. Any docs will also help
William is also correct in saying anything can happen in 46 years, and some guys purposely change things to make it something it is not.