[19Fordy]

After first reading this thread, I fired up my 40 and let it run at a fast idle for about 45 min. until stock temperature gauge needle was on the middle line, meaning Normal. Then, with an infra red temp gun, I took a reading at each of the spark plug cavities on the each head near where the plug screws in. Both cylinder heads gave the same reading of 180 to 182 degrees. The temperature at the front and rear of the heads were almost the same -both right and left. Heads are aluminum radiator is Walker with mechanical fan. Ambient temp. is 67 degrees F. When I bought these heads in 1999 Mark Kirby made them for use without thermostats.
Car was in the garage. Maybe under load on the road things would change.