Emissions Control System ID help, 1971 Duster 340

How do I confirm I have a true-to-original tank? We’ve confirmed it’s an original N95 setup car. Once the correct tank is confirmed I have to get the correct gas cap. Currently have an aftermarket lockable cap on it and want an original. To date, I’ve returned 2 or 3 that were incorrect. Already started another thread about that issue so forgive the redundance.