here is a pic thats might help you, click on it to enlarge

the exhaust will have to come off, and the carburetta manifold to allow access to some more head bolts i believe. You might as well check the valve clearences while the exhaust is off, because you cant remove the rocker cover without taking the exhaust off whcih is a hassle.
Its akward torwuing the engine up, with it in the car very little space as you know.
yes i think they supply the new thermostat hosuing as there was a problem with the old, i had the same paid about £15+ for it from fiat. My temp gauge never goes past half way. So it must be ok.
regards
Chris