A guy on here (formulasullivan) sells the adapter that mounts a 68-70 Charger or 67-69 Barracuda cap. 69-70 gas caps will say Fuel in them thats is engraved into it.
From the thread it seems that 4mulaSvaliant is MIA. No activity since April and not responding to the thread he started. Wish he would show back up! :)