I think the 'plagiarism' claim goes back to an article by my old colleague Tony French that appeared in Pilot magazine. Hard to accept that a brave young chap like Magee could have drawn so heavily on words from someone else, but I am afraid that Tony made a convincing case. He took no pleasure in debunking, at least in part, the legend - but felt the record should be given straight.
You might try taxing the magazine's new publishers with a request for details of the piece!