Suggestions on venting fuel tank

I have a 1973 Plymouth Valiant 318, I am not longer running a Charcoal canister any more since the car is not longer stock. I have since plugged the single vent nipple on the fuel tank. I have a feeling that his is not allowing me to fill my tank up to the max. My gauge is barley at the full but it used to be able to go past the last dash and stay there for a bit. I have taken the filler neck out and noted the level and its the the bottom of the filler neck seal leaving a little bit of tank that can be filled past the filler neck.

Anyway, the only thing I have venting the tank is a vented cap. Ive seen some posts about a 69 Dart filler neck that has a vent that goes down the neck past the trunk floor boot to outside air. Is that a good route to go? Or is there some other ways?

Thanks!