Assuming the coolant level is full, since the overheat occurred at idle, I would check the fan clutch before I dived into the cooling system. (easy to do) Does the engine cool down when you are moving at say 30 mph, or, does the overheat occur at all speeds? With the engine shut off and your hand on the fan, there shouldn't be any forward and/or reverse play (wobble) between the radiator fan and the fan clutch. If the overheat occurs at all speeds its probably not the fan clutch and I would then also look at the thermostat as others have mentioned.
It's not common on Ford V10's but if you have air trapped in the cooling system around the temperature sensor, (or low coolant) you will get a false high temp reading. You didn't say where you pointed your scan gauge to get your temp reading. Always use a 50/50 coolant/water mix.
Chum lee