Question about gas tank vents 4 vs. 1

The early 71 A bodys used a 4 vent tank 11D the late 71- 76 used a 1 vent tank 11E
I have them in stock for $140 The extra line on the 3/8 sender is used for a return line - Hemi & Six Pack
Thanks Vans

So on my '76 Duster, the sender has two lines and then at the top of the tank there is another line. Correct me if Im wrong but it should be as below..

1. One line on the sender is fuel to carb???
2. Second line on the sender is return line from fuel filter??
3. Line on top of the tank going to little plastic unit under passengers floor and then continues on to engine bay is venting tube???

My Duster is was originally a 318 2bbl car and now it's a 383.. It was all running fine up until recently when the 383 went in and the car just doesnt want to take fuel from the filler...

Perhaps it could be something stupid like tank is full and gauge isnt working...????