[Toivo]

No, it actually has to do with the fact that the water jacket doesn't go completely around the cylinder wall, leading to hot spots and trapping steam under the deck surface. Steam holes help release the trapped steam, but the cylinders still experience uneven cooling and actually warp because of it, leading to the head gaskets unsealing and blowing.

I've always heard not to use siamese bores on the street. Maybe somethings different about Ford's design. If so, I haven't heard a good explanation of why, yet.