Actually there's quite a few additions under the bonnet, Gas Injectors, LPG Vapouriser, S-spec air filter, LPG ECU and additional pipes hoses. The standard system still remains in place though.

I'm not bothered about paying for the service in order to keep the warranty valid on the bits of the car not modded. However it might actually end up cheaper just to buy an after market warranty that covers the whole car and use the guy who did the conversion.