Glenn - Your thermostat housing temp sensor may or may not accurately register because the sensor feed wire going to the gauge is so close to the exhaust manifold. If there is enough flexibility to your gauge feed, I'd suggest you relocate it to run along side the valve cover, as far away from the exhaust manifold as possible. I see your original electric temp sensor is still present in the side of the head, just back of the forward leg of your intake manifold.
If you want to double check your temp sensing, you could get an electric temp gauge and hook it up to the sensor in the head and see what it records in your test runs.
