Please help info needed 67 dart gas cap!

Here is the situation I have a 67 dart that I believe had the gas tank replaced with an original factory setup. I want to replace/upgrade the gas cap that was with the car. Old chrome cap has some pitting. The problem is the correct cap when researched shows a "non pressure release" cap. The cap that was with the car when I bought it I believe is a pressure release cap due to the raised up dome in the center on the backside of cap. The correct cap shows no center dome on backside. What do I look for on filler neck or tank to make sure tank is properly vented if I put non pressure release cap on?

Carl