Have to disagree on the Siamese center port idea, a lot of engines from the time period have the same arrangement but not the sound. The only things I see that is distinctive to the Ford flathead is the firing order and the exhaust ports through the water jackets. As an example, the Olds Rocket engine has the Siamese center port, but uses the same firing sequence as a lot of other V8 (same as Ford 289-302). A flathead has a different firing sequence, 1-5-4-8 the four corners, then 6-3-7-2 the four inside cylinders. It may well be the combination of all of these.
Note: Not a new concept, Ol Ron already suggested the firing order.
I was just playing around with the different firing sequences on paper.