Did you show good water flow out the back? If not remove the exit fitting on the manifold and look as well as poke around in there a bit. It is a notorious spot for bits of rust etc to gather and clog the flow.
When/if you remove the t'stat take a good look at what you can see, it just may be time to give her a flush.
The overheating probably is what killed the head gasket if it is overheating so do check the gage or get an infrared temp gun and check~ther pretty cheap now or perhaps someone you know has one you can use. The gun shot at the sender should confirm gage performance if you can't get part numbers.
Good she lit for you, don't change a thing other than playing with the cooling system now one thing at a time
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Dave Neptune