Totally different. You'd have to cut a different shape hole in the door skin to swap them. Also, they look different. The '66-up cylinders sit pretty flat against the metal, whereas the '65 and older stick out quite a bit. They take different key blanks too. The '66 and newer lock cylinders are the same right and left. You just swap over the tail link. The '65 and older have specific right and left hand cylinders. The tail link is riveted on.
