I'm looking for the name of a horror movie or part of an anthology (Chiller/Thriller?) when I was a kid in the 1960's. I just remember a man develops an eye on the side of his neck and it grows into a full-size head.
Could this be The Manster (1959)?
... a foreign correspondent in Japan who is given an experimental drug which causes an eye and eventually, a second head to grow from his shoulder.
Are you sure about the date? Sounds a lot like this film, but it's too late.
The film is a farce about a mentally unstable advertising executive, Denis Dimbleby Bagley (played by Grant), who suffers a nervous breakdown while making an advert for pimple cream...
He then develops a boil on his right shoulder that comes to life with a face and voice. ...
Bagley decides to have the boil removed in hospital but moments before he is taken into the operating room, the boil quickly grows into a replica of Bagley's head (only with a moustache) and covers Bagley's original head,