You got it thats a 71 cap. These are hard to find. They came on 71 abody cars with collision impact protection. They were stopped because of the dome light ignighting the fuel when opening the door after a rearend collision. That little pipe in your trunk is the culpret. The cap is forced off when the tank is smashed. Putting the fuel into the roof of the car to contain it. But when you opened the door you would ignite the fuel. Those four hoses coming from the tank are not vents.This was hushed up and taken out for 72 .Everything was changes so you couldn't put this in later years. 70 on back were all the same but they were not vented. so they changed th size of the ears so you couldn't replace a 71 vented cap with a 71 nonvented . I took a bunch of these caps to Carlisle. I sold them all to one person for $65 dollars each. I kept 2 for each of my cars I do have other year caps with necks. Heres the problem. Some slide in from the outside of the quarter and the quarter has a diferent indent for this. some have 4 holes instead of three. Others are cLocked wrong. a 70 cap and neck will fit use the vent tube because the cap is not vented on a 70. 72 and up will not fit they slide in from the outside. Darts are totaly different the flange is at a different angle. The darts have a flatter quarter Where dusters demons and dart sports have more of a bulge. I used a 71 neck and cap on my 71 duster but I used the vent tube fron the 70 also. This gave a larger vent for greater fuel flow . I run a #8 fuel line.