The 318ci in my daily driven '73 Dart always had the 'issue' it never really got upto temp.
It has a stock 3-core radiator with fanshroud, 7-blade fan with thermo-clutch, but the clutch unit is worn-out and, hot or cold, the fan is just free wheeling along with the waterpump. Can easily be stopped with a newspaper.
Put in a 160°F thermostat and it will run 140-150°F on average.
Put in a 180°F thermostat and it will run 160-170°F on average.

I usually run a 160°F thermostat because the 318ci had bad core-plugs and I wanted to keep the cooling system pressure down a bit to save them.
But last winter when the heater didn't do much and the engine temp didn't even get over 140°F during my commutes, I decided to install a 180°F thermostat instead.

Or I thought so. Silly me I seemed to have forgotten I already had installed a 180°F stat the year before.
So I decided to just change the stat for another 180°F stat, hoping it would perform better in getting the engine upto temp...

I went from a stainless Stant thermostat to a copper Mr.Gasket thermostat from which I had a few used ones laying around.
But it turned out the Mr.Gasket thermostat flowed much more (larger opening even at shallow opening) and now the engine temp was stuck at 130°F during highway drives!

White engine sludge build-up was severe and pretty much no functioning heater in wintertime was no fun either.

Now that I have swapped engines, going from the 8.6:1cr 318ci, to a 11.3:1cr 360ci, and with a 160°F thermostat installed again, the 360ci still hangs around 150-170°F.
Only during warmer weather (80's F) the temp will climb to around 180°F when in heavy traffic.

The only 'problem' I have is my radiator is slowly disintergrating on the outside-front. This is the 2nd radiator in the car that does this.

The copper fins are turning fragile and almost turns to dust when touched. Perhaps the winter roadsalt is taking its toll on the copper of the radiator, or some other (dissimilar) metallic corosion is happening.