Oh, I forgot those questions. Is this a 3.8? If so, (at least on mine) the Shraeder valve (bicycle tire) is located just above cyl #6 ... just below and behind the EGR flow sensor.
I removed and scrapped the clips that hold the injectors to the rail. I wish Ford had used a bit more lubricant on the upper and lower O-rings on the injectors ... they can be very hard, the first time, to pop out or the rail or out of the intake (or heads, I've forgotten which). Once you get them loose, some petroleum jelly will make them much easier to work with hereafter.
Because the lower intake is "wet", it is likely the leak source ... not the head. At least, we can hope.
You may understand why I tend to leave the reservoir cap a bit loose .... so the stopped hot engine, cooling down, is less likely to have high pressure coolant forcing its way into areas it shouldn't be. But then, most of my driving is at 2000 feet, or less, .... so I can get away with a loose pressure cap.