I must very respectfully disagree with John Z. From my experience, if the radiator is too big and the water is cooled too much going through it (i.e. cold ambient temperature, too big a capacity), it will "confuse" the thermostat and the thermostat won't operate within its design limits. I exclusively use the RobertShaw/Mr. Gasket thermostats because they're the best, and I've seen this happen many, many times, especially with the car at speed with a lot of air going through the radiator. A slide rule and a computer may say one thing, but the real world is another. The cooling systems in these old cars are like photons in the subatomic world--on the surface they are what they are--but they don't always behave as the physicists predict. If you fool around with hotrods long enough you learn this very quickly. The 327 low-performance cars came from the factory with smaller radiators for a reason, and it wasn't just because of the corporate bean counters. You can over-science anything, and I believe his radiator is just too big, for what my non-college-degree opinion is worth....chuckle. Good luck, Mikey!