Truck to Cold

[truckin 79]

Anyone else run into this problem, the 79 350 has a 4 core radiator undetermined thermostat. The truck can sit and idle for 20 minutes and heater gets a little warm but not hot. I was going to swap thermostat to 195 but just have not got around to it. The truck has a brand new aluminium heater core. My dad has had to borrow 79 because his truck is in shop and it has been cold in CO the last week, he has been freezing in truck. Is changing thermostat going to make a big difference? I am not sure if temp gauge is working but the thing barely moves off of C when driving around. I know it can be a bad thing if engine runs to cold