My '69 400 has a 190 degree thermostat (factory spec) and the temps run about the same at the heads, a little hotter at the hose, and about the same at the bottom of the radiator.

From the '69 service manual:

A new thermostat (190 degree) valve should start to open at a temperature of 187 to 193, and should be fully open or more at a temperature not in excess of 222 degrees. A used thermostat can be about 7 degrees above or below this setting without adverse effect and should not be replaced.

Unless you calibrated the IR thermometer for the emissivity of the black hose at room temperature vs. heated, and the same for the heads and radiator, the thermometer will not give you absolute readings, but will give you a good indication of whether your system is working as designed. I'm not sure which is the correct thermostat for a '67 400, but my heater is much more effective and the engine runs cooler with a 190 thermostat.