Your absolutely correct, I should have known better when I typed it. Originally delivered to American Airlines on the 27 November 1970 as Boeing 747-123 N9669, it was the 87th Boeing 747 off the production line.
Thanks to your digging on G-HIHO's history, I can say that I flew on it as N9669 American Airlines between HNL and LAX in 1983. The Palindromic registration is what made it stick in my mind. Who was/would have been responsible for the technical side of Highland Express at the time ?