The installation retrofitting Bi-xenon HID H4 units can be a little tight requiring a little modification to the rubber boot that protects the electrics at the back of the bowl. Otherwise I think it's a question of finding £250 and a couple of hours to put them in.
6000k units are optimum for light output, 8000k are bluer but emit less visible light. Look great on a P38. Look at www.hids4u.co.uk for piccies and fitting details.