Engines are designed to run within a certain temp range. Putting in a 160 thermostat logically would just mean that your engine is going to take longer to get to a normal operating temp. A clutch fan puts out a lot more air than a flex fan. Upgrade if you want to run in the 180s. 210 IMO is the edge of safe driveability. 180-200 is fine. I run 185 to 195 normally with my 69 with the stock flex fan. I've got a clutch fan in my 79 TA, and the TA runs at 180 flat with the clutch fan, really hot days it might be at 190.