The thermostat should always be installed with the spring-side facing the engine.

Regarding particular installation on a 2.3L, my Ford Manual says this:

CAUTION: The thermostat seal (8590) must be positioned on the water outlet connection before the water thermostat is installed.

To prevent incorrect installation of the water thermostat, the water outlet connection casting contains a locking recess into which the water thermostat is turned and locked. Install the water thermostat with the bridge section in the outlet casting. Turn the water thermostat clockwise to lock it in position on the flats cast into the water outlet connection.

Clean the upper radiator hose connection, cylinder head and water outlet connection surfaces. Coat a new thermostat housing gasket with Perfect Seal Sealing Compound B5A-19554-A or equivalent meeting Ford specification ESE-M4G115-A. Position the thermostat housing gasket on the cylinder head opening.

It is critical that the correct water thermostat installation alignment be made to provide coolant flow to heater. Insert and rotate water thermostat to the left or right until it stops in the water outlet connection housing, then visually check for full width of heater outlet tube opening to be visible within the thermostat port in assembly.

This port alignment at assembly is required to provide maximum coolant flow to the heater.