Also there is someone in Birmingham that does them. Not sure of the name, but never heard of bad install's coming from them. Definately do some research as price is not what matters with something like this.
As above really, find a good company that can do it. Best get a complete 220 so you can get the engine, gearbox and all the correct mounts. Also you will be able to use the calipers off the car for vented discs, though the 160 conversion would be more ideal.
Quite a bit of work, and would suspect it to cost in the region of £2500-£3000, also you need to allow for more insurance, and the additional cost of fuel.