Early A=Gas Spiller!

Not a problem with my 68 & 69 Barracudas but, it sounds like an air venting problem with earlier cars. My tanks will COMPLETLY fill then the auto-stop will shut off the pump. If I then try to top off the tank, (even just a little bit) gas will immediatly over flow from the filler neck. Likely adding a vent tube would solve the problem on earlier cars! M