Not to deter you from what else is going on, but I had this happen with my Barracuda after I overheated her a very long time ago.
There is a condition called carbon tracking of the head gasket. At some point the engine may have overheated and in the process, smashes the head gasket a little bit more than normal, so when she cools, engine compression pushes gasses through the head gasket ring to the water jacket, and when she warms up she is fine. The temp rising and then dropping is the thermostat opening, if compression is pushing the gasses into the water jacket around the head, it displaces the fluids, the temp goes up, the thermostat opens and fluids rush in and the temp stabilizes.
We have had a couple radiator fixes, purges and such in the past couple weeks, so again, have the front of the car higher than the rear, so air naturally goes towards the radiator. Turn on the heater full hot so it is flowing, remove the radiator cap, fill. Start the car, rev her a few times and let her get warm, the fluid will start to overflow and should run into the overflow tank. Fill the overflow tank between the hot and cold marks, cap the radiator and then watch the overflow just a bit. You should be able to squeeze the upper radiator hose and have fluid go back and forth and see the level change in the overflow tank.
If you put another thermostat in her, do drill a 1/8th inch hole, in the flat part, or at a minimum, depending on your tool selection, poke two nail holes in it. Use the 192 degree stat, which is factory temp needed for the computer systems to function.
Also, if after the above is done to get the engine full of fluids, if you see steady bubbles coming into the overflow container, smell it. It will smell like antifreeze, sure, but if it smells like gas or exhaust, the bad news I started with is happening. Sometimes they will last a week, sometime a month, and retorquing the head will not fix the problem because the seals around the cylinders has been permanently compromised.