FWIW.....I bought the Mike Ray B757/767 Spiral Bound Study Guide. I realize your looking for the B747 input, but his books in general, I found helpful. He keeps it light/simple and easy to follow. One thing that I found in the B756 book, since he is/was UAL, he does tie some of the UAL 'flows'/operations into the book which could be different from your operators flows (as mine was). If your just looking for 'systems' knowledge/layout/explaintions, I'd give it a thumbs up.

Good luck.