If you don't have an engine driven fan make sure you get the right thermostat! DO NOT get the 90Deg. one! You MUST get the 80deg. one otherwise your car WILL overheat!
Also, you must drain your coolant at least to a level below the T-stat. The system is made to have no air in the coolant and thus your t-stat and housing are full of coolant. If you try and just remove the housing, your going to have a BIG mess on your hands!