[hatzie]

High flow thermostats would be the units like the 195°F Stant 45359 SuperStat

To regulate coolant at roughly 195°F the thermostat needs to be fully open at 200°F and closed somewhere around 180°F.
You don't want to run 160°F thermostats in a daily driver. Fuel mileage and engine longevity will suffer. Normal coolant temp should run between 200°F and 230°F. This will keep the engine oil above the boiling point of water to boil off any condensation and unburnt fuel to be exhausted out through the PCV system... These temps will still keep the oil below the temps where it'll start to burn and coke up the engine and the combustion chamber will run at a fairly efficient temp.

The 1970's OEM temp gauge is a poorly calibrated guide at best. Only slightly better than a warning lamp because it gives you a heads up before you get to OMG IT'S TOO HOT. Most aftermarket gauges are little better.
If you really want to know what temps the engine is running you'll need a good quality infrared thermometer. The $30 Lowes, Home Despot, and Horrible Fright units don't qualify. You're going to spend over $70 for a decent one. My old Fluke cost over $130
There really is no reason to trust a 42 year old nail head sender. If it's a new unit it's likely either badly matched to your gauge or, if it's a Letric Limited unit, defective.