I JUST finished repairing TWO 4.6 Romeo intake coolant leaks.
One was so big that it hydro-locked the #1 cylinder. Locked the motor up so tight it couldn't be turned over by hand. I was lucky that the motor wasn't damaged.
The 2nd was a slow leak from the coolant crossover and the heater nipple area. This caused coolant to be in #1, #4, #5, and #6. There was coolant in the valley obviously from the T-stat housing area.
I can promise that these Ford 4.6 intake manifolds CAN leak from way more places than a cracked coolant cross over. The good news is that many are "repairable" with new gaskets and surface cleaning.
Look closely at the design of the cylinder heads. It's easy to see a way that a coolant leaking from the intake manifold can run along the heads and fill the spark plugs holes of an entire side.
Bottom line is the Modular 4.6 intake manifold is easily damaged when over heated. Just having a metal cross over does not stop the intake from being damaged by over heating.
I really can't understand the RUSH to jump to a bad head gasket BEFORE the other and frankly more common causes have been ruled out. Instead of guessing why not do some more testing? I promise you that IF the motor is cleaned up and the spark plug wells are fully dried out, it won't be that hard to see where it's leaking from (if it's leaking from an intake gasket). Do you really want to pay a professional to clean your motor to find a leak?
Further. In the event that no coolant is found on top of the cylinder heads, then that is useful information as well. As in it must be leaking from somewhere else.
Finally. Consider that IF coolant is allowed to stand inside the spark plug wells this can and does damage the COP boot insulator. Which means that sometimes just drying out the spark plug well isn't enough to stop a misfire.
If a blown head gasket is strongly suspected, then go straight to the compression test. However just remember that normally there are other symptoms associated with a blown head gasket. Water in the oil? Oil in the coolant? Running like crap? Miss fires on multiple cylinders next to each other?
EDIT: thinking about it and I can't honestly think of a way that it's even possible for coolant to get into the spark plug wells from a head gasket leak. Just think about how the cylinders are designed and the path the coolant would have to take to get into the spark plug wells from the head gaskets (short of a out right crack).