From what I've read in the past, Ringfire is spot on. Lord was asked, but declined.

McGarrett, however, is mentioned multiple times in Magnum. This incudes the first season when Magnum is trying to figure out what happened to a good friend of his. Magnum was 'broke in' to Naval Intelligence, even though Magnum (and McGarrett) had worked there in the past. So there's that.