If you search in the old forum there was some extensive discussion about mid-2007.
You can install the factory stuff on an X that did not originally come with air, but it is a lot more involved than you would think. The underdash plenum is totally different, the instrument panel control head is different, the accessory drive in the engine compartment would require the A/C mounts for the alternator, the A/C engine pulley, the A/C compressor of course, plus a host of undercar A/C hoses, vacuum lines, the extra resistor for the different HVAC blower in the plenum, and of course a condenser up front.
If you wanted to do the above, the best way would be to have an A/C car at your disposal to compare to as you went along.
A better way overall might be to use the factory indash plenum and controls because they are so well-integrated into the car, and then have a local shop fab the rest.