You should read the book, if you're interested. From the book (p.84):

"Time and time again there appears in print the logical but false assumption that Boeing took its losing military C-5 bid and revamped it as the commercial 747. In fact, the 747 would be an entirely original design that owes nothing to the C-5."

That said, in the same chapter he talks about how GE developed a high-bypass turbofan engine for the C-5 and it was only because they had such an engine that the 747 became possible.

But really my only point is that you should read the book if you're interested.

The engines drive the design.