Vented/Non-vented fuel cap?

Hi all, something that may seem so stupid but, i have a 66 plymouth fury vip 383 that im fixing up. there was no fuel filler cap so i thought id buy one online (as i live in australia and to get ANY parts is a nightmare!), id assume id need a vented cap but having problems/getting confused. I tried rockauto and there was about a dozen different caps. anyone able to give me any advice?

thanks
Author: grimley