A little tip. The thermostat housing is a booger, but I've seen worse. Try working on a Cadillac 500 engine. I used a distributor wrench to pull the bolts without tearing the a/c system apart. Still a booger, a really gooshy (<---fancy technical term) one, but not quite as bad.

 

It's not unusual to get a new sensor that doesn't work. It happened to me.