Had the same problem - the reason was the replacement drive I used - it is thinner than the original one. So I could not get the far side of the drive correctly into the holes for the notches mounted on the drive; that is - the drive was always a little bit too far to the center of the mac case. Everything works fine until you try to install all four screws.
I found a simple solution: I attached some adhesive tape temporarily to the drive cover. By pulling on the tape while pushing the drive in its space the notches slipped into their holes. After this installing the antenna was no problem any more.