Hi, I'm old enough to have been there and its a common misconception that old cars have pressed aluminium number plates, they are a "classic car" invention, the vast majority of stuff licenced over here into the early seventies has built up plates such as the ones fitted on your beetle, into the sixties they had cast aluminium digits that were either clipped or peened on and then plastic digits became the norm either in white or painted silver, these even ran through the seventies with reflective white and yellow backings and black plastic digits, pressed aluminium number plates were a motorcycle thing and became used more on cars during the early seventies but with reflective backings and black digits, the pressed ali plates that many buy today are not typical of what would actually have been fitted at the time.