Proper Thermosts temp for 318

So, the old man and son who worked the engine in my 67 Barracuda have put in a thermostat that never gets above 150 degrees.
Even on 80 degree days, it was barely above 150 sitting in traffic.
And now that the daytime temp is in the 50s, not even near 150. And so, very little warmth from the heater.
My feeling is (rookie) that that is too low an operating temerature for the 318.
What's you take?

I've seen this discussion on another MOPAR site.
"As others have noted, go with the 195 thermostat. The industry moved away from 160 degree thermostats years ago (1950s?), and away from the 180 degree thermostat (IIRC) somewhere in the 70s."