My understanding is that nobody makes a metal housing for the 2003-2006 4.2 AJ34 engine. My recommendation is to get the complete assembly from Jaguar, it includes the plastic pipes, o-rings, thermostat and sensor. It is about $100 and is pre-assembled, which is good considering it is possible to put the thermostat in the wrong way. Also consider changing the hard plastic tube that goes from the tower to the expansion tank. Mine was very brittle and broke during the replacement.

Best of luck. Keep us posted.