Flip top gas cap???

This is the thread you're looking for [FOR SALE] - Ask and you shall recieve! (Flip Top Gas cap Adapter)

And here's the website The ORIGINAL Flip Top Cap Adapter - FlipTopCapAdapter.com

The adaptors are made by @4mulaSvaliant , you'll need a 67-69 Barracuda or 68-70 Charger cap to make it work.