That’s why yours did not have the two small hose fittings originally. 66 or 69, and possibly early 70 did not have the evaporative emission system known generically as the charcoal canister. Or in modern parlance, EVAP.
Sometime around the 70 model year through 75 at least there was a small metal canister mounted to the passenger frame rail under the firewall. Those had the condensing tank behind the panel in the pocket behind the drivers left shoulder and 2 fittings on the rear tank only
The second fitting was for liquid to flow back into the tank after it condensed.
In 77 for sure, but I believe 76 too, in preparation for 77‘s new rules, they changed the location and design of the canister from the metal one on the frame to a higher mounted plastic one up on the firewall over by the passenger side heater inlet vent. This newer design carried through for many years and the product is still available today so we can retrofit earlier models if we want.
On 76 the main tank was the same design as yours, but with only a single vent tube because there was no more need for condensed liquid to flow back to the tank.
This type got rid of the condensing tank inside the cabin in preparation for the new rules dictating no exposed filler necks on the side of the vehicle (hence the gas doors for’77 only) and no more fuel inside the cabin of the vehicle.
Basically you can leave yours status quo if you want and simply Off both of those small fittings.
But if you park inside and especially if you smell a lot of gas normally, you can add the charcoal canister system to yours.
It’s not fully compliant unless you also change the filler neck and To the 70 a later model. But it’s better than nothing.
