[Gearhead999]

Is the fan close to the radiator?? It should be pretty close to the core.

Where is the timing?? Too late will run hotter.

Thermostat or restrictor plate??

What are you reading the temp. with?? Direct reading gauge--Good, electric gauge--Bad.

You may have to go electric....sorry to tell you that. Old Mustangs ran Hot at idle when they were new.