This is no secret , and I`ve posted it a few times .
U CAN RUN A VENT LINE UP IN THE TRUNK, MAKE TWO COMPLETE CIRCLES/360* LOOPS , BACK DOWN THRU THE FLOOR TO UNDERNETH THE CAR ,WILL WORK IN A ROLL OVER , WILL VENT UR TANK W/O FUMES IN THE CAR , upright or not..
I run one on my 68 fastback , doesnt puke gas out when filling , like the brand new 68 barracuda I had when I was a kid .
This is what I was going to say. On my 69 Dart the vent line loops above the filler neck inside the trunk then runs thru the filler neck floor pan gasket to the outside. From the factory like this.