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.