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.
So.......ECS was an N95 option in around 1970. In 1971, it appears as though ECS was standard issue (I have a '71 Demon with NO N95, and it has the ECS system, the same as @Demonx2 ). Here is a picture of gas caps used during the various years. Not sure where I got the pic, but probably from FABO. BTW......No vent tube on the ECS filler neck.

Abody Gas Caps 67-70,70 Cal and 71,72-74,75-76.jpg

You beat me Del!:thumbsup: