What age are the cars?
I did this to a 98 minifcelift CD, fitting the lights from an Elite. There are several versions of the truth on here about what's required. However, I:
1) Moved the headlights
2) Moved the "manual" electric levellers from the old headlights to the Xenons
3) Fitted headlight washers & new washer tank etc
It isn't as factory fit for sure, but an MOT tester told me tht he would pass it if presented, the beam pattern was ok and the levellers worked.
I have all the gubbins to do the self levelling but won't be fitting it as I dont "need" to & the wiring isn't in the vehicles sitting dormant. The Xenon ECU sits in the pointy bit of the o/s front wing, inside the wheelarch - so not the easiest of beasts to get at.
I set up the entire system on a bench and got it all working, ECU, sensors, wiring, levellers etc, so could fit it if I really had to. There is also a single wire connection to the MFD which would need to be replaced/TECH2'd to give the error messages from the Xenon ECU. I got a replacement MFD from an Elite as part of the kit.
Fitting the headlight washers was most interesting as I discovered that my car had previously had a front end bump which meant the bumper support brackets were twisted & needed replacing. You will need to plug in relay to the fuse box and fit new trims below the headlights - in the correct colour.
If for any reason my car fails an MOT I'll just put the old headligts back in.
The wiring is slightly different and has a different connector for main beam supply - which you should remove frm the donor car with about 20cm of cable. The colours are the same so you can solder (dont use scotch bloks) and have the old & new connectors there at the same time aiding replacement in the future. Its really important to solder the joints properly as the Xenons take bout 20amps to strike the arc - this only reduces to the 3.5amp steady state current after a few mins. So coupled with the thick wiring you will need a pretty sturdy soldering iron for the joints - I used a 100watt iron.
HTH