Looks like you are off and running on a nice project. Bummer on the broken bolt count. Lord knows I have busted more than my fair share of them. Not sure about the other ones but the one pictured for the thermostat housing should come right out if you will carefully weld a flat washer to the remaining piece, then break it free with some channellocks while it's still hot. Then it should come right out. You can see how I removed an exhaust bolt from my aluminum head
HERE