I think I got the Mazda all put back together without any problems, but I'm still not very trusting of the work I did. I was going to tap the stripped bolt hole and use a larger bolt on the thermostat housing, but there wasn't room to use the tap without removing the fan and water pump pulley, which requires special tools. I ended up just threading the larger bolt into the hole without tapping it first, so who knows how long it will hold. This time, I torqued all three bolts down to 10 ft-lbs, which is what the manual says to do. I let the engine get up to operating temperature and kept adding coolant to the radiator as the air was purged from the system, and didn't see any leaks so far. Though the temp gauge never got as high as it should, the heater seemed to blow much hotter, but that could have been due to me freezing my ass off in this below-freezing weather and heavy winds. Update: I took it for an actual drive around town just now, and the temp gauge is working like it should now, so the old thermostat was bad. I'm relieved that all this work wasn't for nothing.