There are three different thermostats available for this motor. The original one was a 195 degree F unit. There are also 180 and 160 degree thermostats made for this application. I expect you probably now have a 195 degree thermostat in your motor. I would normally use a 180 degree unit in an older vehicle; and would use a 160 degree unit if the motor had a noticeable tendency to heat up under load. The position of the temperature gauge would be about center with the 195 degree thermostat; and would be correspondingly lower with the cooler thermostats.
Some models in this period came with heavy duty cooling. On those models; there was an electric radiator fan that supplemented the mechanically driven fan. The electric fan is actuated by a thermal switch mounted in the engine; which triggers a fan relay; which then switches battery power to the fan motor. The thermal fan switches and fan relays both are prone to failure. If there is a fan motor on your car; and it does not come on when the temperature goes up; the thermal switch and/or fan relay is probably defective.
If your motor only has a mechanical fan clutch; this type of clutch design often loses friction and slows the fan down as it ages. Such a fan clutch requires replacement.
If the coolant was not mixed with (preferably distilled) water upon installation, this would make the motor run too hot. Some coolant is pre-diluted; but much of the coolant in stores is not diluted. A 50-50 ratio of coolant to water is desirable.
Your motor requires a 15 psi radiator cap to maintain adequate pressure in the cooling system. Old caps can lose spring tension or leak; if the pressure drops, it can lead to overheating.