Harper Carter ... Norman
Why was he uncredited? It was a big enough part.
" Three can keep a secret ... if two are dead "
Yes, it's a shame that his filmography is so sparse because he was quite good as the poor lad who yearned for the affection and approval of his stuffed-shirt father (Clifton Webb.)
It may well be that he was never interested in having a film career; the trivia section in his page says he enjoyed career success in real estate.