Hello. I just joined today so I thank you in advance for any information. My father in law recently passed and left behind a beautiful 1971 Monte Carlo. I'm afraid we don't know much about it and will need to sell it unfortunately. Silly question but how do I tell if it is a numbers matching car? And again I thank you for any help or answers, I really appreciate it.

 

There should be a number 6 or more digits that is on the Frame, the engine block, you might want to begin looking under the back seat for a build sheet. This would indicate the number.
Most of that stuff can be googled and you should be able to come up with it all.